Why has he started ignoring me

This guy is someone who I would consider a friend, we do the same course at Uni and he's part of a little group of us that spend time together at uni. Anyway, I know that he liked me. He's liked me since may ish last year when we went on a uni trip. Everyone in our friend group says it's bright as day that there chemistry between and that we make each other happy. More than anything he's a good laugh to be around and I thought we were atlas friends. He's admitted to liking me a few times, but until recently it had just been when he was drunk and I just dismissed it. Last tuesday (16th) however when we were at a friends party he was talking to my best friend about me for a long time, and said he would want to give things a go with me, but he doesn't think I'm serious. He has a girlfriend, but they both cheat on each other and don't see each other much. That night he stayed at mine because it was easier than getting a taxi back to his, we didn't sleep together. we ordered food and when I was waiting I confronted him about what he said to my friend and said to my face that he did really like me ( I could tell he was being genuine) I didn't say to much back which maybe i should have? but we went to bed, made out a bit and he asked what he can do to make me believe that he was actually serious about me. I said he didn't need to do anything and we went to sleep in each others arms. The one thing thats always worried me is the girlfriend so I didn't want to say anything till I was sure, I didn't want to ruin our friendship. The next day we were texting back and forth just having a laugh, and at one point I did say that Liked him and didn't mean to be funny with him. He said he wouldn't want to ruin our friendship and we carried on texting til sunday morning- most of the time having a laugh. I know he went saturday night, as he told me because he could't be bothered going. Then sunday midday he didn't reply, I didn't think anything of it because we'd been speaking for a few days... Then xmas day I text him Merry Xmas, he didn't open the message for about 6 hours and when he did he didn't reply. It's like he's completely gone off me, but as a friend as well. I don't know why he is being like this and I don't want to text him and pester him? :( All I can think is that because it's christmas and he hasn't seen me he has forgotten he liked me, or that he's been spending more time with his girlfriend than he has in a long time...but then again we are supposed to be friends, and all I was wanting back was a merry christmas text.. not a promise of him leaving her for me, or a promise of him committing. More than anything I want my friend back

I suspect that more than anything you want him for a boyfriend. He has a girlfriend. Why would you want a boyfriend who cheats on his girlfriends. He is not being very nice. You don't need a boyfriend or a friend like that. Move on and spend time with good people.