I seriously need advice! ?

MomOf2 • Married 💏 DD:4yrs old 👑 Angel Baby 5/6/2014 👼 My Rainbow Baby! 5/21/2015 👶🍼💙
I don't even know where to start! 
When my husband and I married, a few weeks after - they (his family) had a family meeting. In that meeting, OUT OF THE BLUE, his cousin (girl cousin) expressed that she didn't like me. LOL. I don't know why and I don't care. She simply said she didn't like me since the beginning. Okay. 
A year goes by, and I NEVER NOTICED IT, I blame myself for that - till one day I noticed she (the girl cousin who doesn't like me) was flirting with my husband, YES HIS OWN COUSIN. BLOOD COUSIN. FIRST COUSIN. HER MOM IS MY HUSBANDS MOM'S (my mother in laws) SISTER. I started keeping an eye on it and yes, it's happened every time there's a family party. 
I'm sorry but it's just getting on my nerves, I've only told my sister about it and she didn't really give me any advice. 
Today though, was my breaking point. I am 9 weeks pregnant and I had a tiny spot of brown/pink discharge that caught me off guard, I was so tired cause this is the SECOND weekend in a row that his family comes over to my house, and the girl cousin comes too. So she started dancing like on my husband, I was so pissed off but didn't say shit cause I was playing it cool talking to someone else. I'm normally not the jealous type. 
This is not the first time though, last time she did this thing with her dress, like lifting it up to almost her vagina infront of my husband and did like a "WOOH" sound while looking at him. 
I am over DONE already. I'm up to my forehead with rage so today I told my husband: "This is the last day your family decides to make my house a play ground, and WTF is up with your stupid cousin dancing on you? Next time she does it I'm gonna fucking grab her by the hair and take her down. You don't mess with a pregnant woman. If she's so horny for some dick she can go find her OWN MAN, in the fucking street. There's millions!" And he just said "Okay and I don't know what's wrong with her."
So he didn't argue or say much but I really don't want this to be a big deal or cause a problem in my relationship. 
Please help! What do I do now?!