Here are my thoughts on this:
First, if things haven't worked out, for one reason or another, with someone you hoped might become a significant other, one of the biggest mistakes you can make is checking their Facebook page to see who they wound up with -- or if they wound up with anybody. I'm speaking from experience here. If you happen to be single, looking at photos of the guy you really liked enjoying happy domesticity, vacations, a life together, with someone else practically amounts to an act of masochism.
However, keep in mind -- as a friend recently reminded me -- that photographs of smiling faces do not always tell the whole story. You do not know if this couple are going to have decades of wedded bliss or if it will all fall apart in a few months [not to be mean, of course, but gay marriages are just as subject to failure and divorce as straight ones].
If it's true that this guy told you he hated you simply because you liked him [and presumably he didn't feel the same], then he does sound like he has some kind of personality disorder, (or is there more to the story) and you are probably well rid of him! He's that other guy's problem now. And if he's supporting the younger man, how do we even know this is a real love match, or if he may come to regret ever hooking up with the unemployed fellow? [Of course, gay husbands have just as much a right to support their spouses as straight ones do.]
But ultimately none of that is important. Your heart will mend. Forget about this guy, stop checking out their Facebook pages, move on, find love elsewhere, with someone who will treat you with kindness and the right kind of passion. You don't need justice, you need a boyfriend!
In the meantime, it's okay to indulge in a little mean-spiritedness. [For instance: In my case, the guy I liked dumped me for a guy who was ten years younger than me. Is it my fault if I can't help but note that his lover happens to look ten years older, LOL!]
For all you know, the younger lover of the guy you liked may run off with all of his money, leaving him homeless and desperate. I discovered that there's rarely any need to get revenge on anybody; life's problems are revenge enough. Besides, was this guy as terrible to you as you suggest, or was it simply that he just wasn't interested? That doesn't necessarily make him evil, although he may seem that way to you.
It's worth repeating that if he was an evil dickhead, you are well rid of him.