Girls with a BIGGER BUTT than you

Ok so my butt is small-medium size-ish and I do a lot of squats recently because every time my boyfriend and I meet up at an event and he's with me, there're always girls with bigger butts and he always look at them.  I get soo jealous but I pretend that I dont see him watching them and I really want to tell him how jealous I feel but don't want to seem b*t*hy telling him so. Any advice?? ?