Partner prioritizing extended family over us

so we were invited to a wedding for a cousin of his that he sees maybe once a year or less. And when we do see this cousin, it’s usually at a family event and we have no relationship with this person and we don’t even talk to eachother. There is no relationship between us and this cousin, we were just invited because he is related to this cousin. Yea he came to our wedding but only to see my husband’s brother and not actually to visit with or celebrate us as he didn’t even speak to us or anything. This cousin has never been a part of our life and doesn’t acknowledge any major life events like the birth of our son, baby showers, or anything significant in life. Not even a text. We literally never speak.

we were invited to the wedding and my husband wants to go but my son and I can’t go due to prior commitments. What I can’t understand for the life of me is why he is always willing to drop everything and bend over backwards for people who have nothing to do with him or his life. He has never had a real relationship with this cousin even growing up but he is upset about the possibility of not attending this wedding because he feels he will miss out on something because “everyone else is going.” I don’t understand why he has always been so willing to abandon me and our son to attend family functions for extended family we have no relationship with. This has happened before and I have tried to ask him questions about why he wants to go and he doesn’t have much of an answer. I have a ton of family in other states I never see and I don’t care to go to any events with them because they are basically strangers to me so I don’t understand why he feels the need to be so loyal and show up for people who don’t even try to have a relationship with him and leave his actual family behind to do so.

has anyone else experienced this? What are some good things to ask him to help him reflect why it is he wants to go to these things so badly and why he would prioritize people who have nothing to do with him and don’t make an effort to be a part of his life when it matters. He said he would miss out on seeing his one cousin that he does have a relationship with, to which I offered taking a separate trip at another time to visit specifically them. But still he feels he’d regret not going and would miss out. But he would also miss out on time with his wife and son? Who I feel should be most important compared to a cousin he has no relationship with ?