My sister walked in while my boyfriend was fucking me from behind and I think he liked it?

okay so this is genuinely one of the most chaotic things that has ever happened to me and I need to get it out.

my sister was staying with me for a few days when I'd just moved into my new apartment. first real place of my own, she wanted to see it, we were having a good time. the three of us, me, her, and my boyfriend at the time, went out for drinks, came home loose and happy, and my sister said she was tired and went to the pullout in the living room.

my boyfriend and I went to my room and I'd been handsy with him all night so things moved fast. he had his hand around my throat almost immediately, the other in my hair, and I was completely gone within minutes. he used my throat until my eyes were watering and then flipped me over and I'm not going to pretend I didn't love every second of it.

doggy, him behind me, going absolutely crazy, one hand gripping my hip hard enough to bruise and the other pulling my hair back, and I was loud, I'll admit I was being loud, but it was late and I thought she was asleep and I was not thinking clearly.

I heard the door open.

I looked back over my shoulder and my sister was three steps into my room looking down at her phone saying something about what Molly posted on her insta story and she hadn't looked up yet and I had this full second of pure panic before she did.

she looked up.

my boyfriend stopped moving. mostly. except not entirely, because he shifted slightly and that specific part of him, wider than the rest, hit exactly the right spot at exactly the wrong moment and I made this involuntary yelp while making direct eye contact with my sister.

she blinked. looked between us. then this slow smile.

"oops" she said, "didn't realize you guys were busy."

she backed out slowly. and right before the door closed fully she looked back one more time. not at me.

door clicked shut.

my boyfriend was silent for approximately three seconds and then went absolutely feral. harder than before, more intense than the whole night had been, got there embarrassingly fast.

I lay there after thinking about that look she gave before the door closed. the way it wasn't at me.

I never asked him about it. I thought about it for the rest of the time we were together though.

Some things you just let sit.