Seeing a guy

So basically I was seeing a guy for two months and he was closeted. This isn’t a problem for me being the way I am I attract a lot of closeted people. So I made the usual things clear like if you want to see girls instead or if you don’t want to do it then tell me and I’ll walk away and forget it ever happened (trust me it’s so painful)Things where going really really great and we where having such a good time together. The. One day he just stopped texting back and blocked me on Facebook which I thought was weird. Prior to this we had had discussions about him coming out as he was feeling more comfortable and we were both ready to fully commit to each other.So he basically just dissapeared for ages then my sister found out he was sleeping with my brothers ex girlfriend who had been my friend for quite some time. Obviously I had no idea any of this was going on but why didn’t he just tell me.Now when I see him walking around he looks miserable as fuck and there’s nothing I can do about it because he chose her and that upsets me 😭I need help to get over this. Anyone out there got any advice that could possibly help me ??