Isn't the clue in the name ,its MOTHERS day ,maybe dads can be included but not necessarily partners .Wouldn't bother me ,does your partner think he should be at every family event?
If her partner went it would have been right for your partner to go. You could have clarified this before going. It's not as if is was a girly /mum lunch out. My daughter granddaughter and myself had lunch out last week as she was working my husband was invited too. He had jobs to do so didn't but at least be was invited.
My son and my Dil invited me for a Mothers day tea,i automatically though my Dh was invited too,and i wasn`t wrong. Bit it wouldn`t have bothered him if the invite was just for me.
Since her partner was going along, I don’t see why she didn’t invite your partner. If she wanted ‘mother - daughter’ time, her partner wouldn’t be tagging along. That’s my opinion, for what it’s worth,
Adult daughter and her partner asked me out for lunch. They didn’t ask my partner and he’s a bit miffed about it. Is this something he should be upset about? I don’t know what the norm is as I’ve been on my own a long time