First be retrospective & introspective.
Why did it happen and was this a good or bad thing done for the right or wrong decisions. What was good about the relationship & bad about it? Assess your and their responsibiltiy for any issues. Then, talk it out and talk often. Seek a close friend, a family member, a mentor, a clergy or a counsellor as needed. Try to see the good in it. Don't dwell.