I want to ask my girlfriend out for dinner after breaking up.

Actually, I feel that the reason why you two broke up with Ben is the lack of communication. The other person doesn't know what you are thinking, and you don't know what she is thinking. Everything is boring, speculative and suspicious. But since the breakup didn't hurt each other too much, there is no need to make it so complicated. Treat her with a normal heart. Treat her as a close friend, and don't care too much when you break up. Put it down with mutual respect.