better to have loved and lost..?

I feel so numb right now... I've made the decision, with good cause, to leave my boyfriend of 4 years, my first love, my first everything. Its 3:30AM and I cant sleep, I have school but I cant think, I dont want to think because none of my thoughts on this situation seem at all rational. Im sad not for having caught him in an attempt to cheat situation but more so because he's gone. I'm honestly hardly hurt maybe because he was drinking and he didnt actually persue this later but he left a paper trail a mile long that quite clearly showed his intent and I just decided enough was enough. On top of all the general issues we've dealt with as a couple this year, this act of disrespect was the straw that broke the camels back. I love him so much though I almost feel as if theres absolutely no way this is truly happening. He wants to make it work and well he says all the right things I cant help but feel as if I've made a good choice even though its completely distroying me on the inside. I just want to pretend like nothing happened but I cant, I cant be that person who just turns a blindeye. I want to be strong and believe that theres someone else better for me and although I'm sure there is I just can even imagen who. When I was younger I use to be able to visualize who it was that I might end up with one day but now those visions do not come all I see is this person who has hurt me but who I care very much for still. Question, can you still befriends with someone you've had long term relationship with? and if yes how long does it take to get to that point, ballpark? I just want the best for my ex even though I should hate him I know he just needs to grow up and unfortunately I cant help him with that and in some way that kills me because I had hoped that maybe I could.