[...] Solved for now, but future is arising.

I can't help you, but boy does it make me glad I'm happily married. :D

Let the toxic relationship run its course; the guy will eventually dump her. Tough to watch, but either she has to want to end it, or it has to be ended for her. Not much you can do otherwise.

I don't know what advice to give, but it must be tough to watch someone you care about go through this.

First rule of relationships: stay out of everyone else's.

Live and let live I say, if people have already told her she deserves better than that's all you really can do. It'd be worse to encourage her to do something she doesn't want to do.

We accept the love we think we deserve.

You don't need a man to make you happy, the only one who could do that is yourself - or at least that's what I always say to my friends. Does she have any other hobbies? I know it's not that easy to forget a guy, but if there's anything else that she likes (or you think she'll like) then show her that so she knows what it's like to truly be happy. Am I making sense? Also, don't let the guy end the relationship first. Her doing it herself might give her some closure (and improve her confidence).

People will make and learn from their own mistakes in life. Interfering with someone else's relationship is never received well. Just let her know you care for her and you're always there for her and when she needs you, be there for her.

You shouldn't care this much, she is the only one who can definitely change her life, there is nothing that you could do or say to change her if she is that blind into that relationship...
Also, as our friend up here said "Life goes on. Time passes by. people change.", this sums up the situation very well, you have to keep going with your life, time will heal and make her forget about all this sh*t and as so, she will change and maybe you wont even be friends no more, but don't worry, that's how life work's, people come and go =)

I'm not an expert but I think it's better to let her figure it out herself, it seems like you can't change her mind. It kinda sucks but there's not much anyone can do.

People who are in abusive relationships often need help getting out, even if this relationship ended naturally, it could further feed the depression. However it's not sure that you are in the position to provide any help first hand. If you care, then consider offering your support should her need any, like someone else suggested, but trying to pry them apart forcefully is unlikely to succeed, may even have ill consequences on your relationship with her.

Maybe you could try getting her to contact a professional who could help with the depression, and that would in turn improve her general psychological situation, possibly leading to her slowly recognizing the toxicity of the relationship she's currently into.

No good will ever come from trying to break up a relationship. Best to be there for her when it falls apart on its own accord.

if she has depression she probably needs help and can't face breaking up, or wants to know/realize she's being cheated... maybe she's more secure living that lie.

or maybe she's just stupid enough to remain near that guy, who knows. *facepalm*

You can't help people that push you away and refuse help.

Sounds like your obsession with her is just that you want to rescue her. If she was normal you wouldn't think twice about her.
If you REALLY want to be with her, just tell her. Make it quick and to the point.
I've liked you for years, I think we should make a go of it.

If that doesn't work then definitely forget about her and move on. You've been emotionally unavailable for at least one year while you've been dreaming about her. Not fair to yourself or any other women you may have been talking to during that time.

inferiority complex. talk to psychologist

All I can say is stay out of her relationship. It is hard to watch her breaking apart on her own. But all you can do is be there when she breaks. I think this is the best thing you can do now.

I've made countless suggestions to women in similar situations, but no matter what useful advice I gave, they decided to not listen, and kept going back to bad situations. it's their choice

I think that the answers from random people probably won't be that helpful. Consult a good psychologist if you want a better understanding of what to do.

My thoughts on this is that the guy provides an anchor for her, shitty as that anchor might be. Being without a relationship and in her current state of flux won't necessarily be better for her well being. So if you know someone nice who likes her, replacing the current relationship with another one would be a good idea, but if not, it may be better to just leave her to her current one.

I'm not an experienced person about this
But
I think most of the comments said "Don't interfere too much, let her decide"
While I agree with that
You and with others help should teach that guy some lessons
A bad guy like him could hurt others.. More and more
He'll become a cancer in society

Or if you're thinking it's too much work, just don't think too much.. I guess
I'm overthinking it xD

View attached image.

You're not fooling anyone, just ask her out already.

As someone who was the "depressed girl" in a relationship like the one mentioned: it will pass. Either the dude will find another gullible girl, who he prefers more; or the girl will see that it won't work out, on her own. The latter is easier if You have friends. Friends being around helps, but don't parrot always the same thing about the dude being a bastard, else You might alienate her.