She knew I like the guy, yet...

A close friend of mine recently had a fling with a guy I really care about a lot. She knew about my feelings for him but went ahead anyway. When I asked her about it, she told me they were both adults and had decided on a consensual relationship. I asked if she thought it was a nice thing to do, and she apologised but said it was my problem because she didn’t think she had done anything wrong. Should I still be friends with her? We have known each other for years but if someone doesn’t care about my feelings, does it even matter if she is in my life anymore? She thinks she did nothing wrong, which is why I wonder if I am the one who is being unnecessarily childish. What should I do?
Your friend is right about the fact that she had a relationship with an adult, which means she wasn’t the only one you should have a problem with. You are absolving the guy completely, which isn’t fair to your friend. What you are right about is figuring out that this isn’t someone who has your best interests at heart. No one says she can’t be with someone you like, but to do it while knowing it may cause you pain —irrespective of whether the guy in question reciprocates in any way — shows that your feelings don’t matter to her as much as you would like them to. If her friendship matters, you can always stay in touch, provided you are aware enough to know whether you can count on her or not. Will she be someone you can turn to in a crisis? If not, maybe you should re-evaluate the strength of your friendship.

We broke up over a misunderstanding and I don’t know how to convince him that I did nothing wrong. How do I fix this?
If there are no open lines of communication and he isn’t willing to listen, there isn’t much you can do until that happens.