Erection While Being Penetrated

I usually am half erect when I start to slide my dildo in my ass, by the time I open up and accept it all I am rock hard. Then sliding it in and out rubbing against my prostate it feels like the head of my cock is going to explode, so I keep working until my prostate milk starts oozing out of my head, I like the way it tastes, its a little different than seamen. Starts out kind of thin but as I keep going it gets thicker and looks like cum.
So I keep going to try and get a prostate orgasm but once the milk stops flowing my prostate becomes less sensitive and I cannot achieve it so I jerk off with my dildo in my ass which gives me a leg shaking orgasm and produces a large amount of cum.

 

I got an erection when my female kink buddy confessed she wanted to watch me being fucked by another guy. I have never engaged in this before but the idea obviously turns me on ( as long as a female watches)

 

I was fucked by a guy for the first time quite recently. It was in front of two women. I have a rampant sph fetish and the experience was so arousing that I didnt just get hard I came while he was doing me.

 

For me its just the position. If I am bent overgetting it doggy I can get a chub but that is from the swinging motion. On my back I cannot get hard but if the top knows how to fuck I will end up cumming on my stomach or at least leaking puddles of precum. If I ride cowboy facing him I can stay rock hard and cum all over his chest