Dark souls games! Yeah, they can be pretty tough, but they are fair (for the most time) and their difficulty isnt hard just for the sake of it. Instead, it pulls you into the game's world and it really makes you feel like a regular knight that murders hundreds of enemies. Took me 50 hours.

Also, try Binding of Isaac: Rebirth if you are into rougelikes and don't mind some violence, gore, gruesome creatures and the mockery of religion.

I'm sorry to hear about your breakup. But I assure you, these two games will definitely make you forget about her!

Dark souls series, or Dota, though it will only change your heartbreak for another kind >.>. Witcher 3 is awesome though, if you'll go thru everything, awesome story, translated audio books are a good time killer as well

S.T.A.L.K.E.R. games can take some time and you can run them with a toaster.
Dark Souls, Fallout new vegas, Divinity Original Sin, Dragon age origins, Baldurs Gate/Icewind Dale, will also probably take some of your time

If you want an absolute time sink, then you should get into MMOs. Lord Of The Rings Online and Guild Wars 2 are both free2play, not p2w and pretty good.

XCOM 2 or XCOM EU + EW, Civilization V, Big Pharma

League of Legends was one of the tools I used to get over my last break up. However, I'd highly recommend to just try and meet up with your friends as much as you can, it has a far greater effect of getting over someone. Remember, hoes go, bros stay.

Don't Starve can be quite addicting and most fun (imo) when played for long periods of time.
Stardew Valley is a very calm, relaxing game if you're into life/farm simulators like Harvest Moon or Animal Crossing.

Hmm yeah looking at my games I realised I don't have many calm games. Most are either fast-paced intense or can be frustrating/require a lot of concentration or you die a lot. Normally when I'm stressed/in a bad mood I watch videos on youtube of people who are comforting to me bc I've watched their videos for ages. And then normally I'm in a better mood afterwards and don't mind playing w/e. haha Hope you're able to get over your ex soon and be happy again, good luck. :)

Buy Mountain

TERA.

Shit, that game will hook you like Captain motherfucking Hook playing tag while covered in super glue and riding a motorized scooter equipped with turbo nitrous. If you're into that kind of thing, of course. But yeah, the game is free, great, and extremely addictive.

WHY would you play dota when Heroes of Newerth is the BEST moba!? You realy should play HoN instead when it comes to mobas tenosuke sir...but as for lenghty long time to complete games...theres alot to suggest and im not sure what would you like to play.

Blasting trough Need for Speed Hot Pursuit 2, Most Wanted and Carbon, aswell as the Race Driver Grid games, Flatout games and Burnout games can REALY take alot of time, which is good because their amazing games so thats a option i realy recommend.

If youre willing to discover the amazing'ness of famous, well known, iconic, any good strategy games out there, id like to suggest for you to try and play trough every.single. one of them, of them i mean a list of many games i can tell for you to dive into, it will be a lot of time spent but i gurrantee you, you wont regret it, their realy good games, such as Warcraft, C&C, Starcraft, Age of Empires, State of War, KKnD, Commandos, Act of games, Z games, Ground Control games, Cossacks, Stronghold, Warhammer 40K Dawn of War games and etc. and etc. and ofcourse all the games in their series, it can be a good ride :) and once youre done with the campaigns, you can use i believe Hamachi or Game Ranger to play any and all of these games on multiplayer with still many active players to play with and against, forever. CNCNet for example is a website and software you can use to play Westwood's many strategy games unchanged, online, OpenRA is a suitable choice aswell for a different expierience.

You could seek out any and all horror games and games that start with dead, old and new, to, ekhem, familiraze yourself with creatures youve not seen before and locations youve yet to visit like Dead Rising games, Dead Space games, Silent Hill games, etc. and mind you, their not short.

The Sims games can be played for a realy, realy long time, make a family and, well, live, as long as you can and if it stops, just make a new family or take control of the many other ones :) endless waste of time if you stay with it gurranteed. Otherwise watch miss lifesimmer waste her life playing nothing but Sims on youtube.

If you want to head into deep uncharted waters, putting effort into playing emulated PSP and Sega Mega Drive II/Sega Genesis games can REALY pay off cause i know alot of good ones but again, i dont know if you want to get into that. If youre willing to try them, il happily donate my time to list all/most of the good ones that are a must try and you can be assured it will take heaps of time to get trough of.

Armorgames.com hosts many wonderfull flash games and i so happen to have favourited a list of pretty great ones, im quite picky so you can rest assured that atleast most of them will be a pretty great or good try, dont underestimate flash games, their still games and great devs make them, and its ofcourse not just that place, nope it isnt. For example The Last Stand Dead Zone can suck up good amounts of time, aswell as all the good games combined such as Sonny games, Raze games, Sift Heads entire series, Kingdom Rush games, Crush the Castle games, etc. and etc.

A viable option would be to complete as much as you can the fighting games of Ultra Street Fighter IV and Mortal Kombat 9 (Komplete Edition). Try to complete the game with all characters and fighters, reach and see everyone's ending, unlock everything you can, it will be fun and it will be lenghty, a good time :)

Old games such as the original Fallout games, Diablo games, Arcanum of Steamworks and Magicka are going to take ALL of your time away if you decide to play them, big worlds, many things to do, many ways to play, its awesome. Fallout 3 and New Vegas are wonderfull choices aswell, ive spent combined over about 500 hours at the very least and STILL never fully finished them, i mostly didnt go after the main questlines because i liked exploring and doing sidethings, helping people, trading, customizing, scavenging, talking and simply enjoying the game, its a ideal game, all of these are, to get lost into and coming out of them very, very, very late.

Getting into picture making by using Garrys Mod and Source Filmmaker can be a neat idea if you feel like expressing your imagination and creativity, wishes and ideas, you can see the many examples on steam, deviantart and else, heck, you can spend alot of time watching amazing gmod videos that i could happily link to you, albeit not all of the good great ones unfortunatly as i lost my youtube account from which i could find them with ease, its a realy good time to spend if youre looking for action and laughs and stuff.

Streets of Rage Remake is a wonderfull place where you can REALY spent a huge chunk of your time on by completing the game with different characters, different paths, achieving different endings, play with a nearby friend, and when youre done with the base game which by the way is all three games combined, you have the option to download and play trough the many, many fan created campaigns and levels of their own made up stories that feature custom backgrounds, levels, different looking enemies, it offers good replayability.

Alot of pretty good online games are a gateway to massive amounts of time possible to lose upon such as Counter Strike games, Crimecraft, Defiance, Super Monday Night Combat, Infinity Wars, Killing Floor games, Tactical Intervention, OpenRA, World of Tanks, Armored Warfare, War Thunder, Warframe, Path of Exile, Planetside 2, APB Reloaded and just about a whole lot of else other F2P games on steam and off steam that you can see for yourself, look and give everything a chance, esspecialy to Nosgoth as its going to be closed in the coming time saddly.

World of Warcraft is endless, it was made to suck you up, too much to do, too much to achieve, too much to try, too many places to play it in, could be for you.

And if you cant afford some titles and goodies, im sure you know what the next best alternative is in getting to play them and no, i dont mean skipping them entirely, their worth the play trough, hope this helps.

Since Bethesda games are off the list, I would say maybe a game like Borderlands 2, Torchlight 2, Van Helsing : Final Cut, War Thunder, World of Tanks, Elite: Dangerous or Euro Truck Simulator 2 if you really want to just relax and chill (I didn't think I would like a game like Euro Truck Sim 2, got it in a bundle, and have well over 100 hours into it already).

Other option is do what I do. Watch for bundles, and buy way more games than you can possibly play. Then when you're in the mood for 1 thing, you can play that, if that doesn't work for you that day, find something else.

Pillars of Eternity.

it depends on your taste

The Swindle is quite the addictive thing

Well, what kind of game do you like?

There are some stellar suggestions here already, but without knowing your preferncr:

Strategy: civilization IV, total war series, crusader kings 2
RPG: witcher series, baldurs gate 1+2, fallout or elder scroll series
FoFootball manager

X3: Terran conflict

Dragon Age: Origins, Fallout.

Warframe. You can grind all the loots to your heart's content. :3

Looking at your Steam profile, I see that you are part of some anime related groups, but you don't have any anime games.
If you're willing to try something new, I'd suggest you to try Hyperdimension Neptunia Re;Birth1.
It might appear weird, but this game really helped me overcome depression, and made me a better person overall!

Minecraft. WoW.

The Witcher 3, took me 80 hours just to complete the main storyline, really amazing game, just not really fond of doing side missions, otherwise it would've easily taken me close to 150-200 hours

tales of maj'eyal very good roguelike, i already spend more than 400 hours in it. And if you try to get all achievment, you probably spend eternity on it.

Witcher 3, I've played through it twice and I'm on my third playthrough now. Plus the second expansion is coming soon which is apparently bigger than Witcher 2 (I think that was said at some point don't quote me)

I got really hooked into This War of Mine recently, I enjoy it a lot.

But probably Witcher 3 took most of my "single player" hours, so I can recommend that if you for some reason didn't play it yet. And both previous ones too.