Most Helpful Guy
I am in a very similar situation with my girlfriend. I think what will help most is being very clear that you're sorry but you're doing what you need to do for yourself and your own happiness, additionally it would be easiest for you if you didn't talk to him right now.
Most Helpful Girl
If you still want to be friends set some boundaries and tell him about them. But he's your ex for a reason, and just because he's heartbroken doesn't mean you should baby him and try to help ease his pain. It was your choice, and if he can't accept it than that only makes things worse on him.