We Shouldn't Be In Here Doing This

I have a female friend who is best described as being a tomboy despite the fact she is thirty two. She has a short hairstyle, for ease of maintenance she says, wears denims or tactical trousers because they are comfortable and and has a lot of under armour t shirts that cling to the body, she has very tiny boobs. She isn't a lesbian and has no interest at all in girl on girl sex...but she loves gay male porn as much as she loves hetro porn.
We have never fucked, never gotten close to fucking, never kissed or thought about it. We have slept together in the same bed butt naked, she has been to swinger parties with me and watched me with other women and i have watched her with men and she has seen me with other men, i am Bi-ish when the moment takes me, and she finds that very hot and admitted she wanked off to the memory of it.
I jokingly said 'So next time i visit a sauna do you want the dirty details of any encounters' she said 'Yes Please'. After that she kept asking me anytime we met had i been recently. I jokingly said i'll take you to one in the other city and she was game for it.
Now as i said she has very small boobs and could pass for a guy in the semi darkness of a sauna especially in the steamrooms or dry sauna. Anywhere else where a towel isn't worn and she would stand out for not standing out.
So i said okay. The sauna in the next city was better as it had cabins on the same level as the sauna and steamrooms, no worries about communal changing areas then, and darker corridors in that area as well. So off we went one Saturday. We booked into the sauna and the staff didn't give her a second glance, we got into the cabin and got naked and then i had to pull her towel down, she had wrapped it around her chest like a woman, no guys wear it around their waist as we don't worry about our chests beong on show.. So with that we ventured into the steamroom.
It was very steamy thankfully having just gone through a heat up cycle and there a few guys in there. we sat down together and watched what was happening. One particular guy had a massive cock and was sitting there stroking it for all to see. Another guy was fingering his ass and the others were watching the show. The massive cock guy was eyeing up my friend and i had told her about the silent language of the sauna and she wisely averted her gaze away and he got the message but i felt like teasing her a little and had my cock in my hands wanking away and big cock guy liked the look of this and came over to me.
We stood facing each other in the swirling steam wit each others cocks in our hands and our lips locked together in a kiss and our other hands fingering the others arsehole. From the corner of my eye i could see her watching the show and slipping her hand underneath her towel. Big cock guy went down on his knees and sucked me off in a very noisy blow job and after a few minutes stood up for me to return the favour which i did. as i sucked him off i kept peeking round at her and she was eyeballing me back clearly enjoying the show. I fingered big cock guys arsehole as i sucked him off and he was enjoying this a lot as his cock got stiffer in my mouth and i felt as though he was going to cum, i then started massaging his balls and he started to face fuck me and grunt and moan and then he pulled out and jizzed over my face and chest, big lumps of jizz spalttered on me. I stood and wiped his jizz off me and flicked it onto the floor and he turned round and bent over a bench and offered me his arsehole. I slid my cock up there and fucked him hard and fast but i was looking at her and she was looking into his eyes as i was fucking him...her hand was up her towel fingering herself like crazy and when i spunked over his arsehole he kissed her and went off to shower. I sat beside her and asked her what she thought of it so far. She whispered into my ear " Take me into the cabin and fuck me". So i showered off the jizz and joined her in the cabin. She was spread out on the little bed naked with her fingers in her pussy wanking herself. I asked her if she was sure about this and she "Yeah, do me because watching that has made so fucking horny". So we kissed and then i put my cock against the lips of her c**t and with a look into her eyes i slid it in balls deep and we fucked on that little bed, missionary into doggy into spoons and then she got on top and rode my cock hard till i blew my load. We lay there facing each other afterwards. 'Well' i said 'Now what ?'....'Fuck me in the sauna' she said and then let's try the darkroom.
We did....oddly no one really noticed and she even BJ'd a guy in the dark room as i was doing her from behind.