Not trying to be petty.

So my old best friend is my sister in law. I use to think we were close and cloe like sisters. But as time passed by especially after I got with her brother who is my husband now she started to change & just wasn't he same. But I tried to be the bigger person and good hearted person and still try to make this friendship work. But everything changed in the past two years especially in the last three months. She became friends with some chick, she was always a HOE and proud of it, she even tried to sleep with my cousin for exchange on getting a free oil change. But I didn't Judge I don't say notbing. Her friend her decision. In December last year she invited This girl to my birthday celebration to a lounge. I didn't care I didn't mind, but my husband and this girl exchanged number. Yet this girl knows who I am, knows we are married knew I was right in front of her while my husband asked for her number & didn't have not one ounce of respect to be a woman & say " your married" no the hoe that she is, gave her number. Long story short, he left me after that weekend said we weren't working out gave me so many excuse and I was just surprised. Well it was cause for a whole week that he left he was with her. So bottomline my husband had a affair with this girl didn't last cause he knew he messed up & came back to me asking forgiveness blah blah. So my " bff " knew what happened & of course not her problem and she was upset about it too. But how can you still sit their and still be friends with this girl ? After me being your so " bff " even sister in law and still have a friendship with this girl ? When I confronted  her about it she said that my problem and problem with that girl has nothing to do with her. I tried to confront the girl about it but she was to chicken to be grown and tell me what was going on. But she was chicken to post on snap chat how she was all over him & how he came to her cause " I wasn't keeping him happy " lmao which I find hilarious cause she really taught she was going to be the next MRS ? . But the point of this is I don't want her near my child , cause we are going to have a baby. Which I'm not with him at the moment cause of everything he's done in the last 3 months which is a longer story. I don't want notbing to do with his family beside his mother cause she on my side. I don't like that he's cool with his sister after knowing what he did with her friend & knowing that she still friends with that girl. Which my husband isn't with her anymore cause he wants me but am I being petty ? Or immature. Cause to me this is far disrespectful and I'm a high person on respect.  But I don't want them near me now or ever my child.