SO's family.

So lastnight we had a party with his family and there was family there that i had not met yet, he introduced me to a lot more of his family. Well anyway, he has a cousin (lets call him cousin A) that brings my SOs ex anywhere that my SO is, frusturating!! So we decided we will not be around cousin A bc he is doing nothing but jeopardizing our relationship. Now, his other cousin, (he will be cousin B) asked me for nudes through snapchat while me and SO were seperated & cousin B had a baby on the way. I told my SO and we stopped hanging out with cousin B. Before me, A & B were like my SO's beatfriends. they did absolutley EVERYTHING together. Okay, now Cousin C, was there lastnight and i had never met her. She started talking mad shit ahout me infront of And with A & B and my SO as me and SO walked past them. never met this bitch in my life, she would say shit like "Slut", "Yall are fucking gay" (we took a walk to the baseball fields) she said "Dont think you're making a home run tonight, skank!" Anyway, my SO didnt say a word to them. just kinda blew it off. Am i wrong to be upset about this?