Rude cousin

So I was at the mall with my bf and we ran into three of his cousins. They were talking about a party on Saturday that they’re going to. And when we were leaving one of his girl cousins said, “Yeah go to the party so you can find a different girlfriend.” Then she continued to say Just Kidding a bunch of times. My bf said, “Yeah don’t go putting ideas in her head.” In that moment I didn’t get bothered as much. But it just really hit me right now. And I just needed to vent about how mean that was. And how my bf didn’t defend me. 😞 i don’t know how to block this kind of stuff from getting to me. Any advice?