I think if you cheated on your boyfriend and fancy someone else then you can't really be in love with your boyfriend. It wasn't meant to be. I think you should bite the bullet, tell your boyfriend, and then be single for a couple of months.
Just because your "friend" slept with you and says he likes you doesn't mean he will leave his long-term girlfriend for you. To be honest, he sounds like a complete sleazeball and not someone I would personally count as a close friend. Firstly, he cheated on his girlfriend, secondly, he took advantage of a girl who was drunk, thirdly, that girl was you, a girl who was supposed to be his friend.
It's quite possible that your feelings for this "man" have only come about due to the "exciting" nature of your encounter with him and the comparative tedium of your current relationship. If you were to embark on a relationship with your "friend" it is likely your feelings for him will fade. Why has it taken you so long to fancy him? Quite a coincidence it happens after your drunken fumble.
Telling your boyfriend won't be pretty. In fact, it will be painful, and he will probably go ballistic, as he is entitled to. But in the long run, he will be grateful for your honesty and letting him come to terms with it. And it will help you move on too. I guarantee that if you do not tell your boyfriend, this will eat and eat at you for the rest of your life. If you have a conscience or indeed a soul, you will tell him. For the first few months after telling him you might feel a bit rubbish but you will heal and it will make you a much stronger person.
I would hope that your "friend" tells his girlfriend too. It's possible your boyfriend might let her know, unless they don't know each other.
Finally you really need to assess what you look for in a friend and in a boyfriend.