I got a pretty specific taboo fantasy haha
I get home from work early one day and I see a car in the driveway. My heart starts to race as to who it could be, so I quietly enter the house and check all the rooms. I hear what sounds like screaming coming from the In the bedroom, only I find my girlfriend riding a tall, muscular black man with a massive BBC. I creep up to the doorway but I can't bring myself to interrupt them. I see how much she's enjoying it and hear how loudly she's screaming and I begin to get hard. That's when my girlfriend spots me in the door. At first they jump, startled from seeing me, but then they freeze for a second, not sure what to do. My girlfriend notices that I'm really hard and asks how long I was watching her ride his dick. A smirk comes across her face as she resumes riding again. That's when she tells me that I should get closer if I want to watch. I obey and slowly start to approach them, almost entranced from seeing my girl being stretched by bare BBC. When I get close my girlfriend makes me take off my clothes and she'd shows me how much bigger a BBC is than my babydick. They laugh at me while her bull mocks me, asking how badly I wish I could fuck her like he can. I'd have nothing else to do except for to serve her and her lover - I'd hold her legs back while she was getting fucked, rub her clit while she took the BBC, get them water... I'd help however I can. When he fucks her too fast and he accidentally slips out, I would lick him before sticking him back inside. Sooner or later, he'd start getting closer to cumming. I'd beg him not to cum inside my girlfriend, but she'd make me shut up and demand he breeds her. He slams his cock as deep in her as possible as start pumping - his balls twitching as they unload. After a short while, he'd pull out of her, leaving her swollen red pussy filled with his cum deeply inside of her. Finally, my gf sits on my face and makes me lick out every drop of his cum from her pussy. Afterwards, she tells me that she can't go back to my small white cock and that we're going to be doing that more often.