An entirely theoretical conversation I was having with my partner. Curious to know what other people think.
It you go for a ladies’ night out, and leave your spouse at home, and then when you turn up, your friend(s) has brought their spouse or invited one or multiple men along on the night out, it’s courteous to message your partner and ask if they’d like to join after all.
Similarly if a man goes out with the “guys” and turns up and his friend has bought he wife, or invited other women he’s friends with, it’s courteous for your partner to message you and invite you to join.
DP wasn’t disagreeing with me, incidentally. It was just something we were chatting about.
YABU - no need to tell your spouse and invite them just because others have brought their partner’s or friends of the opposite sex. Carry on as you were
YANBU - as the group dynamic has changed, it’s polite to let your partner know and give them the option to come and join you.
Obviously there are extenuating circumstances.