Most Helpful Girl
If the guy broke it off with you and wants to be friends it's for three reasons. Firstly, so they don't feel like a 'bad guy' for breaking it off with you. It's a way to soothe the guilty feeling they have for hurting you by ending the relationship. The second, main reason they want to be 'friends' is so they can keep up with what you are doing in case their new fling doesn't work out. Finally, they think they might have a shot at some ex-sex if they hit a dry patch, so it's worth keeping you around for. Seriously. That's all it is.
If you broke it off with him, it's pretty much the second reason still, but he hopes he can find an in with you down the road. Exes don't really make very good friends unless you were already friends before you dated. Even then it's not usually possible to be friends right away because there are unresolved feelings on one end or the other.