It doesn't cost anything except a few breaths to say "Happy Mothers Day". It's crazy as hell to me how many times I saw this same situation go down on Facebook yesterday from women in relationships with men who couldn't be bothered. When I was growing up every woman who looked old enough to have children was wished a Happy Mothers Day on general principle whether stranger or family by both men and women.
People who care about each other observe niceties to make the other person feel special or appreciated. If the man you are dating didn't wish you a Happy Mothers Day knowing good and cotdayum well you have a child(ren) then he's a
savage and doesn't deserve further access to your time or vagina. If it was me, I would ask him why he didn't say anything and THEE only right answer is that something traumatic happened to him or a loved one on that holiday. Any other answer means he's trash and should be discarded.
I have not been in the habit of telling women to leave men but I'm starting to notice that these dudes are getting more and more out of pocket with micro-aggressions and disrespect very early on when they are supposed to still be on their best behavior which leads me to believe it's only down hill from where these women are finding themselves in their relationships.