I'm probably being silly about this, feel free to tell me if i am.
DH's brother and SIL split up a few months ago, he had an affair with a woman from work after years of treating her like shit. Apparently he told my DH that he had been meaning to split up with her multiple times over the course of their relationship but "things always got in the way" (things like living abroad together, buying a flat together, having a baby together...) I don't know the specifics as my DH infuriatingly never asks for any details, but I know it wasn't an amicable split and now BIL is living in a different flat and having responsibility for their son for half the week etc.
It's my nephew's birthday coming up and I'd really like to get in touch with ex SIL, particularly as her son and mine are of a similar age. We're not particularly close and don't have a lot in common, but we get on quite well and she's a lovely person. Previous to them splitting up we'd text on occasion, and video chat with the boys playing etc. I don't want to lose contact with her just because my brother in law is an idiot, but I know that the split has devastated her and if I contact her it might be upsetting.
Any advice or similar experiences would be appreciated!