My husband and I have his ex-wife over for Mother's Day and go to her house often with the rest of the family for Easter, Thanksgiving, Christman, etc. I don't know about "friends" in the sense that I-pick-you-to-be-my-friend, but I do not think one should try to rip someone out of their life just because they are not part of it now. My husband's ex-wife is mother to his children and grandmother to the grandchildren. I have an example of it both ways as she burnt her bridges with my husband's brother's family so we often have awkward holidays where a big chunk of us have to go to two parties, etc.