My ex-bf's girlfriend walks around in her underwear?

Okay so my ex-bf and my current boyfriend live together along with another guy they know. Its happened twice where my ex's girlfriend walked around in a shirt and her cheeky underwear. Once she walked right in front of my boyfriend. I'm not jealous, she does have a good butt. But it's a respect thing. I don't run around wearing no shirt. She has a good butt and no boobs I have big boobs and an okay butt lol. So I know what she's doing. I was thinking I would give her a taste of her own medicine and wear a sheer top super low so you can see a bit of my bra. I don't really talk to her boyfriend, I certainly don't flirt. My boyfriend has told me she is jealous of me. I have no idea why, I'm not doing anything! What should I do?
My ex-bf's girlfriend walks around in her underwear?
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