How do you feel about your ex-girlfriend who caused a break-up with your girlfriend?

We broke up because my boyfriend went to see his ex-girlfriend when she asked him for a some kind of help. I told him not to as she could ask someone else, but he didn’t.He even went lunch with her afterward. He is a history, but I am wondering how he feels about the whole thing(any regrets???) and his ex for ultimately causing our break-up. What do you think?