These are the things he shouldn't be telling you
You already feel bad, you don't need to know the details of what his sadness is doing to him. It's not fair to you. You should tell him that soon you guys will need to not talk for awhile, a month or so... just to get used to not leaning on each other. Its a hard adjustment, but there is one thing he needs to realize, the one who caused him the pain (no offence) cannot be the one to fix his pain. In other words you comforting him from the pain of you breaking up with him will not help him in anyway at all to move on.