AIBU or is FIL being unreasonable?

[Ibiza7]

I get on great with both my in laws, however they don't have such a great relationship. Married 50 years but constantly squabbling but no intentions of leaving each other. He adores my daughter and today calls and asks if he can take her out for the day to a farm at the weekend. He doesn't drive and says a friend is going to take them and when I ask who replies "Don't worry (daughter) knows her". when I press him he refuses to say who only that 'she' has a daughter the same age as mine. I tell him that I'm not comfortable with the situation and do not want to get involved if he's got a girlfriend and my daughter is definitely not going to be involved. Its.not fair on her, she's only 9, or my MIL who she's equally close to. He gets the hump and hangs up on me and now I'm sitting here with his secret and not knowing whether I should tell my husband or not. My Dad treated my Mum very badly and I'm just really uncomfortable with the whole thing. AIBU?

I wouldn't keep that secret from my husband if it was me. Also obviously YANBU to not want your DD involved if FiL is having an affair. Although I wonder if Mil actually knows about it? If FiL really wanted to keep it secret it sounds mad to involve a nine year old.

I don’t want to read and run on this but I don’t think you cannot keep this secret to yourself, if I were in your shoes I would tell my DP.

Tell your DH, I wouldn’t keep it a secret.

Definitely tell your dh!

It doesn’t make much sense to bring her along to a family event if it was secret. I would suspect that she probably is a “ lady friend” but that your MIL is probably aware. If she isn’t then your FIL is being dramatically blatant. That being said I wouldn’t make a big dramatic statement of “ I think your dads having an affair “ but “ do you know who your dads friend is who’s coming to the farm with him?” If your MIL is aware I would let them get on with it .... including the farm trip if your DD wants to go of course - she doesn’t need to know anything.

MIL hasn't got a clue. Have spoken to husband now and he had an idea due to something said, over a drink, at Christmas. Agreed withe me that no way was daughter going to be involved but thinks we should stay out of it, for now, in case it's something and nothing.

YANBU tell your husband don't go keeping secrets.