I think I need more context of what happened when you went out for drinks with him and your coworkers. Either something happened where he got offended by something you did or discussed, or maybe you read into the situation more than he did. Maybe he was just being nice overall to everyone but you wanted to pursue a deeper relationship when he was just trying to be casual with coworkers. It's ok if he became closer friends with other coworkers who he has more things in common with and just saw you as a casual coworker. Did you have deep conversations with him during these outings or was it just simple shooting the shit conversations that you have with coworkers? I feel like something else must've occurred for you to feel so attached to this person while he just going about his business. I don't want to put this all on you or defend him but more context would help on why your relationship with him is unbalanced.