I committed a really big mistake by sleeping with an another guy
You keep changing your story. In one post you only kissed another guy. The above quote is from another one of your threads, in which you admit to sleeping with another guy.
You aren't being honest with us, are you being honest with your ex?
Yes, ex, because he's made it perfectly clear that he doesn't accept your apology, that he can't trust you, and I don't blame him one bit.
You went to a party, got drunk, got stoned, cheated, and now you're blaming everything and everyone for this mistake, but you aren't truly blaming the only one that is responsible. You.
You are the only one that can choose your path, you have the power to stay faithful, or to cheat. Are you sorry that you cheated, or sorry that you got caught? Are you remorseful for your actions, or upset that you couldn't get away with it?
I've said it before and I'll say it again. The ball is in his court. He doesn't have to forgive you, that's his choice and only his.
You can say your sorry until you're blue in the face. The time to think about how this would hurt him, was when you actually had the chance to avoid hurting him, not after.
If he forgives you then consider yourself lucky, but don't expect him to forgive you just because you're sorry.
Get over yourself pity, leave him alone, let him heal, give him the chance to make up his mind about you.