Long story - here's the quick version.
My Step-Dad (DSD) had a very bitter split from his XW who went out her way to make his life difficult financially and regarding their daughter. He'd been advised to always try to sort details of both between themselves and not involve courts. The agreement was that he have his daughter every Sat and one weekend a month.
Sunsequently he married my Mum. My DSS never once stayed the night and most Saturdays XW would call with some excuse; DSS was busy, she wanted to see her friends, she was ill, she didn't like my Mum etc.
Cut to many years later and DSS is staying with my DM and DSD after falling out with her mother and went out clubbing, got drunk and when DSD called to find out where she was she was very upset and told him that she'd waited every Saturday for him and he hardly ever turned up. DSD puts this down to drunkeness but it has bothered me for years that maybe the XW has canvcelled my DSD's visits but hasn't told her daughter in order to turn her against him.
DSS is an adult now and married with her own DD and is now much closer to her father. He wants to leave things as they are for fear of upsetting her but I can't forget about it and want to say something. I like her very much but we're not close. I'm thinking of e mailing her husband who's lovely but not sure it's any of my business.