If you believe someone has betrayed you, are you still obligated to them? And does it matter if that person is a child or an adult? Does the bad behavior of another mean you are free to behave however you want at that moment?
I think it comes back to two major considerations. 1) how your response will cause you to feel toward yourself and 2) Whether or not you really understand the situation and the people involved from a dispassionate place.
If you are wondering what to do, talk it over with a safe person who is not so close to your situation. If you don't have anyone like that, or you feel you have already leaned on them too many times in the past, it may be time to talk to a therapist, clergy member, mentor or other safe outside person.
Have a Good Week,
Cheryl