Just got scammed for the first time :c

I had Manhunt, which I was trying to trade cause I got it in a bundle with Bully. So I went to Reddit where they have Game swap and I thought I'd try to trade it there since it was a steam key and not a gift. So here I am, trying to trade the game and FINALLY someone wants to trade! I was so happy because all the game was doing was sitting there and I had no intentions on playing it. He offered Guns Of Icarus Online and I've been wanting to play it for so long, so with all the eagerness, I said ok lets trade! Well he then puts the key in chat, I copy it, and me being the nice guy I am, said "here you go!" and gave him the key, then he says, "This is only redeemable on Capsule :(" so again, me being the nice guy I am, told him I would not redeem his game until he downloaded Capsule to play it. But he refused my offer and said, "No thank you, I don't play games on Capsule, I only play games on Steam :/".
So I got a little nervous as I thanked him for the offer and went to go download Manhunt on Capsule just to make sure. But I get there and guess what! There isn't anywhere to redeem key's on Capsule and plus the bundle said, "Third party DRM: Steam". Once I sat down and realized what had just happened I got the most depressed feeling ever.
Just an idea of what I mean, last week I had 4 expensive bills hit me in a surprising way(New to living on my own)leaving me with hardly any money, then I go to the Dr. because I have some health issues going on only to find out that I have to come back in a few weeks to get checked for Diabetes (I'm 21, male, and only weigh 120lbs so Diabetes was the last thing I thought could be wrong) and then to also get checked to see if my kidney's are still ok since I waited so long to go to the dr(no insurance).
I'm not here to start a pity party but to only warn everyone else of how fowl people are. I realize that trading steam keys isn't such a smart thing to do. I realize that not everyone was raised to treat others the way they would want to be treated. I just feel like bad luck rides on my back everywhere I go and getting scammed is the one thing that did not need to happen right now...