I actually have experience with this, thanks for the thread.
I remember her going out with her girlfriends a lot during this one winter, maybe 3 years ago. We were driving around, about to get some coffee when she started acting weird and nervously asked me the question that's burned into my head for years.
>what's up?
>*frustrated sigh* user, can I have sex with my friend?
just like that, not flirty, not sexy, it was a frustrated, heavy way with which she spoke.
At first I wanted to make a joke out of it and say something dumb like "lol, just let me watch" but I could tell from her body language that it wasn't a joke. she wasn't even looking at me at this point. All I said back was "why?"
she explained that she's been wanting to "experience" something like that for awhile, and that her friend was the one who brought it up and she really wants to do it in private with her, no pics, no one else there.
After a bit of driving around, I agreed, and drove her home. We didn't talk for like 2 weeks week after that.
Once we saw each other again I was blunt and asked her if she had done it already, she just looked off to the side and said a simple "yeah". I asked, "So how was it?, did you get what you wanted?".
She told me that she felt uncomfortable talking about it, but I saw her ever so slightly bite her lip as she said that.
Long story short, she liked it, and asked to do it once more since then with the same girl before she moved pretty far away. Since then she's never brought it up again.
Our sexlife stalled for a month or two after her first experience, but it's been back to the same thing since then.
After years she's opened up and told me she just wanted to know how it felt since her friend apparently had a crush on her and she wasn't sure if the feelings were reciprocal.
After all that, we're still doing just fine.