How do you know he regrets the break-up?

Answer 1

he will call you or try to apologize in person. if he doesn't do any of those look at the way he acts around you and around others. some men might be slow to talk about it compare the way he currently acts to how he used to before the breakup if he seems not himself then he most likely regrets it and wants to get back with you but he might not have the guts to tell you so talk to him and find out.

Answer 2

You will notice that she keeps talking to you, finding out what you have been doing, how you are. She will most likely flirt with you, or tell you how she has met someone else, to make you jealous and see your reaction. Best thing to do is flirt back or ask to meet up, if she flirts back or agrees, than you will find she is probably regretting breaking up with you