Short version:

She (let's call her Zoe, a clear 10) and I have been good friends for a long time (~3 years), in the same circle of friends. Last week I ended up in bed with her (not what you think). I was stifled and clueless how to properly escalate without risking too much. Did not want to cheat on my GF, and scared to destroy the friendship with her. How should I have done it??

Long version: (For medium-long version skip to "Ok, here comes the gist:" ; p)

I met Zoe about three years ago through my circle of friends. Clear 10, not just by my standards, very popular. She was in a relationship, I was single. Her relationship did not seem in a great place because her BF seemed to travel a lot and was gone many weekends. There was immediately chemistry between us and whenever we hung out I would get IoIs like she touches me on the knee, brushing stuff off my shoulder (even in front of her BF), laughing at all my unfunny jokes etc. But on the other side she never gave me too many or too overt IoIs where I would say ok, I can definitely make a move.

We went on several 1:1 "dates", some of them initiated by her, but it never really went to overt IoIs from neither side. Those dates could also be viewed as just friends hanging out. Most of the KINO from my side all very playful and did not show too overt interest: like giving playful hugs, picking her up and carrying her, taking hand for a few seconds, piggyback, small touches while talking, stuff like that. She seemed open to all that, did not talk about her BF while we were hanging out, but I never made a move that would escalate more.

Thinking back, I should have made a move during that time! I was too scared though because she was in a relationship and we have close common friends. It turned into a friendship where we would hang out once or twice a month, often times with groups. Then I got together with my current GF. Together now for the past 2 years. During all this time Zoe still together with her BF. Currently, between me and my GF things are not great, I have a strong desire for Zoe and like her alot, but also do not want to break up with my GF right now (it would hurt her bad and I still have some hope for the relationship).

Ok, here comes the gist:

Two weeks ago Zoe broke up with her BF. She told me about it. Last weekend Zoe, me and a group of people went on a roadtrip. My GF was on travel. We rented an AirBnB with limited rooms/beds. Mostly couples plus Zoe and Me. So my friend suggests "why don't Zoe and you take the room with the kingsize, is that ok with you?". Zoe: "yeah sure, no problem". Me thinking: "holy shit". We go into the room, I joke around a bit. Then we end up lying on the bed (clothes on) chatting. She wants to check something on her phone and goes into a doggy style position with her ass facing me while she is checking her phone. WTF, IoI!?! We rejoin our friends. At night we go to bed. Me only in underwear, she in long yoga pants and a tight shirt (IoD?!). We chat for a while about how her relationship broke, and I tell her I have some doubts about mine. No KINO from my or her side, just chatting for like 30min. Then she suggests to sleep.

I sleep on my back. She turns to her side facing me with our heads separated by only maybe 20 inches (50cm). She closes her eyes. She could be lying much farther away or turning her back towards me.. IoI!?!

I was thinking the whole time how I could escalate without risking too much. How I could slowly test forward and judge the "temperature". But I figured if I touch her in any way it becomes completely clear and overt that I want be sexual. Also, I did not want her to think of me as a cheater.

How would you have done it? I feel like I missed a huge opportunity. It's killing me.