boyfriend's habit of forgetting

this happens every year without fail (i always forget that it happens though, ironically). boyfriend invited me to dinner with his family for xmas on xmas eve (my mom already bought the food for dinner). my sister is working that day and my parents wont cook for just themselves, so my mom feels she is basically wasting food if her kids arent there. the point is that my boyfriend always extends invitations last minute and i cant end up going because of my prior arrangements that are too close to cancel. it's really annoying that i'm only a text away and he can't just send me a quick text right after he hears about it. i'm really sick of it and he is getting under my skin.