<human>: So I've recently been getting closed to a few new friends who are in a  monogamous relationship. Through discussions with her (21F) I've learned that she wanted an open-relationship at the onset but accepted that he (21M) wasn't open towards the idea. Ever since we started hanging out together she's been a bit touchy-feely with me, which I've never been very comfortable with, but I have tried to ignore it. 

Recently I learned that she's unhappy sexually in the relationship, and I tried to offer advice, mostly about open communication with him and how to do so effectively.

 She admitted that she has brought up the idea of opening the relationship and that he accepted as long as it was with someone he trusts and knows. I quickly pointed out that it seems like he's just agreeing to keep the relationship and she readily admitted that was likely the case. While she didn't exactly ask me to be the third-wheel, her behavior and language heavily implied it. 

My issue isn't whether or not I should consider this - although I find her attractive I have no desire to have even the potential for drama to pop up - but what can I do to keep things amicable with everyone involved? I don't want to lose them as friends, but I also don't want to potentially mess things up by openly confronting this issue. I also feel that my being close to her will potentially ruin my relationship with him if he starts to feel insecure or threatened.

Can you condense the text into a few key points?
<bot>: I think my friend's GF wants to sleep with me, I don't want to ruin all of our friendships and don't know how to handle the situation.