Is it necessary to keep someone in your life as a friend if they do not respect your boundaries?

My family has repeatedly left me out on occasions, last occasion I wasn't invited but I was expected to be there, I didn't go now my uncle wants to know why, should I confront or remain silent and let go?
How can you show someone who is upset that you care without making things worse for them? What actions or gestures would make things easier for them?