It's certainly possible that your friend has some attraction to guys. It's also quite possible that he was just drunk. I don't think sexuality isn't nessessarily static. I mean it can be subject to a little change depending on the situation, the person your with, the amount of alcohol you consumed, etc. So, I don't know if I'd read too much into that.
To danbk, it seems like you still feel pretty bad about what happened with your friend. I don't know if it would be best to reopen old wounds, so to speak, but maybe you should talk to him about it now. You say that if you could go back you wouldn't have done what you did. If you told him that you still regret it maybe he would be able to understand your feeling a little better now and it would improve your relationship. I don't know him or anything so I'm not so sure that I'm giving good advice... maybe it would be best to leave it alone and let things go as they are. Just a thought though.