Maybe you should.. you know, not keep in touch with your ex-girlfriends? I don't see how that would end well for anyone. If you break up with someone (or they break up with you), that usually means they're not good for you, so you shouldn't be around them in any way.
Would also help prevent problems with a new girlfriend later. "Who's that girl?" "You're still talking to your ex??" etc.
~ The loveliest rose can hide the cruelest thorn
I love you ♥