What are your ages?
Is today when you told him you wanted to end things?
What were the imporvements? do you mean imporvements just today?
Are you still intimate with him?
If he's showing a different side of himself and it seems like he may be working on changing the things that you don't like, then you might at least want to give him a chance and see how things go. Maybe you telling him that you wanted to end the relationship woke him up and he doesn't want to lose you. There's nothing wrong with giving him a chance, just keep in mind that it's not that easy for people to change, so its possible he could just be doing this to keep you. Time will tell more than anything else. I welcome your thoughts, let me know if you want to talk more
There's no way to know if he is being honest with you or if he's just telling you what you want to hear. There's just no way to tell. The only thing would be to start back off as a friend, and get to know each other more on that level, before jumping back into the intimate aspect. If you continue to sleep with him, without knowing what he's really getting into, then you're taking your chances. It's hard to know what's going on in someone's head, but the important thing is to not listen to what they say, but what they do, because actions speak louder than words