My sister split up from her DH 7 years ago. It was instigated by her and was pretty unexpected, though I knew that she'd been unhappy for some time. They'd been married for 20 years so we knew my BIL well and he is DS2's godfather.
Ever since then she has found being in social situations with her ex-DH very difficult. It has meant that we've often had to choose whether to invite her or him to parties etc, which has meant that he's been excluded. She has told us that she finds it 'odd' that we want to stay in touch with him, as she has no interest in keeping in contact with any of his family.
As the years have gone by things have got slightly easier, but Christmas is still a sticking point. They share custody of their children, which means that they do Christmas Day on alternate years. This year she has the DCs on Xmas day and BIL has them on Boxing Day. She wants to spend Boxing Day with us, but thinks that BIL might ask if he can also come and see us with the kids. Her view is that we should tell him not to come if he asks, because she'll be there. She told me I should tell him to 'f* off and spend time with his own family'. I don't think she meant it, but the sentiment is there.
I love my sister - we are very close and I never want to make her feel uncomfortable. But at the same time I want to stay in touch with ex-BIL - we get on well with him, and he is, after all, the father of our nieces and nephews and our son's godfather. He seems perfectly comfortable in my sister's company - he has a new partner and has 'moved on'. (My sister has a partner too btw. She also gets on well with her exDh's new partner.)
Advice please?