How I [23M] got into a sexual relationship with my roommate [28F] [MF]

Before we get into the story, a little bit about myself – I am 23 and recently moved to Chicago from New York.
Now since i just moved to Chicago, I found this okay-ish apartment in my budget . But the reason i chose this was because of the people that lived in it . I met them and we felt connected vibe instantly. I live with one girl, who is 28 year old and she has a boyfriend who comes over regularly and another 23 year old guy.
So this story starts a month and a half into after I moved in.
The girl, lets call her Amber, and her boyfriend – lets call him Sam – they both share an open relationship. But its different from the actual open relationship, and by different i mean they only sleep with someone else when one of them is out of town or is going to be busy for a few days or weeks. A fact which i learned in a very awakening moment. In the most literal sense.
So one night I wake up to take a piss and i come out of the room to go to the washroom which comes after the living room – while my room opens directly into a part of the living room. And as i open, i see Amber naked on the coffee table with a guy on top of her , who is not fully naked, he is though only wearing a T-shirt. Since our house is out on the main street, the street lights come in through the window and just lit up enough of the room to be partially visible.
Amber has always been a moaner, and someone who talks a lot of dirty while moaning. I could always hear her demanding Sam to fuck her harder and demanding him to fuck her pussy in a sentence such as “fuck that pussy hard. Make that pussy squirt”
She is also loud during that, and unapologetic about it. During the first day we met, while i was still prospecting about it , she said,
“Before we go forward, i should tell you me and Sam have a lot of sex – and by lot of sex i mean pretty much every night. And i am a moaner . So hope that not disturbing for you.”
I thought how loud or how much sex would they have honestly. But spending the first night itself, i was proven wrong. Now probably my other roommate probably doesn’t get her moans that much, cause his room is farther away from her, but for me she is right next to me – sharing a wall.
The first night I unpacked and slept on the bed thinking I’ll finally catch on some sleep with a full day of moving, and as i lie down on my bed, i start hearing the dirty talk of how she wants to suck the life out of his dick and the slurping noises begin followed by loud gag reflexes and his moans.
Now i wont lie, the fact that i am so near to someone having sex, with every sound being very audible, it made me feel as if I was part of a threesome where i am only watching them get down and dirty.
But i am still prioritising on my sleep even though at this point my dick is slowly getting hard. But then i reach the point of no return. And that is when he starts going down on her and she starts moaning.
Now i have heard my fair share of girls moaning . But this was something different. It was almost like i was listening to a porn movie . The moans were amazing. It only took me a second after the first moan i heard to get rock hard.
She kept saying “lick that pussy lick that pussy good. Put all your tongue in it”
And before i knew it , i was holding my 8 inch rock hard dick in my hands. Hearing her moans put me into a place where i did not realise when i had started jacking off. But she wasn’t done, this moaning went on for another solid 15 minutes before she exclaimed, “i am gonna fucking cum!! Open your mouth!! drink that fucking cum”
At this point even I noticed my pre-cum to ooze out now. I was really turned on. I wanted to cum. And i did pretty quickly once he started fucking her. And her moans and dirty talk reached to another level.
Now they must have had a good solid 40 mins of fucking before he came on her boobs (she kept repeating that for the last 5 mins when he exclaimed ‘i am gonna cum’)
And it got really hardcore in those 40 mins .. the bed was shaking she was moaning a lot- the pace never got slow, he only kept going faster and only stopping (i am guessing) to change positions.
I remember i came twice that night . Once when they were having sex and one after they were done and they slept but i was still very hard as i w take out to moans from my head . So i jacked off again – and that was the first time I fantasised of how her body would be . I did notice the hourglass figure when i came the house first time , and i also noticed the noticeably bigger than average boobs she had and the tight round ass she walked with. And this night was first of many (and by many i mean every night) that i jacked off her moaning first and then second time fantasising that i was the one fucking her.
Before moving here, i hardly masturbated once or twice a week, but now a month into living here, i was masturbating twice every night.
So now when i saw her on that coffee table with her legs wide open and her hands holding her boobs and playing her nipples with one hand while rubbing her clit with the other while the guy fucked her as hard as he can, i got an instant boner. While i am a guy who loves to sleep naked, i wore a pair of boxers when i got out of the room to take a leak. And as i saw her boobs, and her hard nipples, there was a huge tent formed on my crotch and as she noticed me and my tent, while i noticed her big , 34D full boobs jiggle up and down with the motion of the thrusts, i quickly noticed she saw me enjoying the view, so i quickly went to take a leak and once i took a leak i noticed to hear the moans again. Till now she wasnt moaning, which cleared a confusion that i had over the month that maybe she is faking it with her boyfriend of how big he was and how hard he was all the time, and that how much cum he was shoot. But now i realised that she was faking it in this moment and not before .
And now that i had seen her boobs and she was moaning, i was rock hard again, and i felt that i had to jack off . So did, i couldn’t hold my cum too much this time, the image of her boobs moving up and down and the fact that she was looking at my boner was too much for me.
While i walked back, i noticed he was done and he was lying on top of her and she moved her to see me as i was walking back to my room. I noticed her eyes went down to my half hard boner as i walked to my room and gave her a smile before going in, and she did the same.