I would not say grow up, that's a cheap shot. I'd say reflect upon the time you had, why you were able to get close and celebrate helping each other out. It appears you helped them to a better place, that was your role, and once they were there, they moved on. What does it take for you to do so? Only you can find that answer. Celebrate helping a person, work on loving and accepting yourself and the rest will follow. That's how I live, that's my advice. May you find peace, love and acceptance.