My Boyfriend (19M) called our friend (29F) A MILF and I (19F) don’t know how to feel about it?

One of my boyfriends bestfriends got a girlfriend who’s 29 years old, who has a child. We make jokes about how he’s a stepfather now and must take responsibility, My boyfriends bestfriend is 22 years old. I’ve gotten close with said girlfriend and chilled with her a lot. She’s a very nice women and she treats me as her own daughter. One day him and his friends were all hanging out and laughing, I was there just listening in and joking with them. When my boyfriend of 3 years and one of our other friends comes and makes a joke to me and everyone else, how his 22 year old friend is just dating a MILF. I didn’t like that. There was a rumor before at their job that, His bestfriends girlfriend and my boyfriend, we’re screwing. I know my boyfriend would NEVER do that. But the fact that he called her a MILF, touched me the wrong way. I understand if he was calling her pretty or just joking around, but the way he was just coming off set me off. I don’t know if i should tell him, or just leave it be? I think i’m overreacting, but my stomach keep getting that sinking feeling.