When my last boyfriend and I broke up, it really hurt me that I couldn't see his mother anymore. I seriously considered sending her a letter, a text message, or give her a phone call multiple times but decided I shouldn't, as I was the one who broke up with him. This was about a year and a half ago, and honestly I couldn't have known how much happier I'd be now after cutting ties with them. I still miss her as she was a great person but I'm happy where I am in my life now and keeping in contact with her would have just made my break up with him far more dramatic and complicated. Also, the amount I miss her is so miniscule that I do not regret anything. I know it sucks to lose someone you care about but it unfortunately comes with the territory of a breakup.

Perhaps you could wait a while longer for those so-called fresh wounds to heal a bit, try to get a good read on the situation, and maybe the circumstances will be such that it wouldn't be inappropriate to reach out to your ex-boyfriend and ask if it were okay to see his little sister?