<human>: Can you summarize the given text in a few sentences?

I've known my friend Ben for 5+ years. He's been dating Stacy for 4 years, and they make a pretty great couple. I met Stacy through Ben, but very rarely talk to her outside of parties and small get-togethers. 

Stacy has been acting pretty inappropriately towards me and I'm not sure how to proceed. Outside of a little physical attraction, I'm not interested in Stacy at all. There were three parties that Ben/Stacy both went to along with me and my friends where she made advances towards me (verbal and physical) that I'm pretty certain are inappropriate. While she hasn't said anything that solidifies any of my theories or incriminates her in any way, there are things that really raise a red flag. How should I proceed? Ben deserves to know, but I'm not sure it's worth the shitstorm that could arise, along with possibly crushing a 4 year relationship. I guess I'm not certain that my concerns are completely justified?

As a note, I didn't specifically include what she did to me physically, because I didn't feel that it was 100% necessary, but it's borderline sexual.
<bot>: friend's girlfriend is acting inappropriately both physically and verbally to me, not sure if I should bring it up with my friend.