The best thing you can do is cut your boyfriend off -- at least for a while. He either hates your guts because you broke his heart or will want to get back together with you. Either way, your staying in his life right now is only going to make things messy.
Wait until he establishes a solid relationship with someone else and is done being angry with you, then you can be friends. This is the only way to go, unless you want to make him (and you) suffer.
You sound like a fickle brat. Enjoy your new plaything and leave your poor ex alone.