No way!

You finally break through the sheer eroticism that is heavy in the air, and you break yourself through, almost yelling: "No way! This lesson is about grinding, and teaching positions, I won´t let you fuck Alyssa! That´s cheating!"

Sid sighs heavily: "Well, I´m disappointed in you, Matt. Allowing this would have been a sign of great trust between you and Alyssa. She clearly trusts you, and you clearly don´t trust her."

Alyssa looks disappointed as well. "Mmmmfff...maybe just this one time...?" Sid still has his cock perched right up against her entrance, partially sunk in to her pussy already...

You: "I'm not gonna let Sid take your virginity, Alyssa. There's no way!"

Sid slowly pulls the very tip of his cock out of Alyssa."Well, that's a shame, Matt. This could have been a breakthrough in your relationship with Alyssa..." He says, now just rubbing the head of his massive cock against her clitoris.

You: "I don't see how you fucking my girlfriend improves her relationship with me...."

Sid: "I've already been fucking her mouth, in a sense. And now you and her are more sexually connected than before..." He says, now sliding the shaft of his massive, wet, cock against your girlfriend's wet pussy.

Alyssa: "He...has a point...mmm.."

You: "Yeah....but, still...I should be to the only one having sex with Alyssa...."

Sid: "That's such an outdated way of thinking, Matt....you should grow up..." He places the tip of his cock against Alyssa's pussy entrance again. "Not gonna change your mind?"

You: "No..."

Sid: "Fine...."

Now Sid starts really sliding his cock against Alyssa's pussy folds, trying his best to stimulate them both. You, happy with them obeying your request, start jerking off to the rhythm of Sid and Alyssa's grinding.

The sound of wet flesh grinding against wet flesh is.... disgustingly erotic, and the smell of their .... almost....sex, fills your nostrils, fogging your brain. After a while its like you're a part of this, enjoying it as much as they are. You can imagine Sid's hairy ass to be yours, as you stroke yourself to completion. You cum first with a moan, then Sid looks close.

Sid: "ughhh....I'm gonna cum all over your girlfriend, Matt! Watch as I cum all over her precious pussy! Grrhhhaaaaa"

You: "Wait, don't come on her pussy!"

But it's too late, Sid's first cumshot is so powerful, it shoots up on Alyssa's breasts. His second reaches her navel. The third, fourth, fifth, sixth, and seventh all went straight on to your girlfriend's pussy, as Sid pulled himself back and aimed his cock down.

Sid: "ugh...I really hate cumming into the air like this...."

Alyssa seems disappointed "ugh...I didn't cum....this sucks."

Sid: "Believe me, If Matt had let us fuck, you would have cum like never before..."

You: "I'm sorry babe, I just couldn't stand to see him fuck you..."

Sid: "Maybe Matt can make you cum with his mouth, would you like that, Alyssa?"

Alyssa: "Well...he's never done it before....and I'm still really horny.... sure!"

Sid: "Hear that? You're a lucky guy, Matt."

You look at your girlfriend, body absolutely soaked in sweat and Sid's dirty homeless cum.

You: "Can you clean yourself up first? Sid's cum is all over you."

Alyssa: "Sure, I can walk to the bathroom naked, covered in Sid's cum, past all the roommates. Would you want that?"