Some more ground rules, but for Monica

You lean back in your chair, almost toppling over. It takes you a few seconds to understand what Monica had just told you. The initial shock turns into confusion, then even anger. What does she think she's doing?

You allowed her to mate with your girlfriend. And just as you had started it, you could end it at any time.

She better be grateful to you. You give her access to Amy's Pussy and how does she thank you? By trying to get your girlfriend pregnant? How cheeky can a person be?

"You all right?" you say, getting up from the chair.

"Or did you hit your head while fucking?" You walk towards Monica. Just before you reach her, she actually takes a step back. She didn't expect such a reaction from you.

"I allow you to satisfy my girl and this is how you treat me? Are you serious?" You are now standing directly in front of Monica and looking her in the eye. She is taller than you, but her previously imposing posture has now diminished.

"Hey man, all I'm saying is that I've had a few kids in the past with women who really wanted it and..."

"And you decide that for yourself?"

Monica is taken aback. Usually, the cucks give in immediately. They usually beg, too, which does turn Monica even more on. She underestimated your backbone. She remains silent.

"So listen..." you begin. You're pissed. Like, really. But then you think of Amy. Monica is her best friend. You definitely don't want to ruin that relationship. And there is also...

"Monicaaa sweetie? I'm waitin'! Where's that second round you promised me?" you hear shouting from the bedroom.

Seems Amy is happy. And that's worth more to you than anything else in the world.

"..Amy appreciates you. She likes you and she seems to like having sex with you. And I'm sure you care about Amy too. But in order for us to get along, a few things have to change."

You start telling Monica the rules:

1. You get invited and don't just show up. If Amy wants to see you while I'm out and you're sleeping together that's fine, but you don't just show up unannounced.

2. You are, after all, a guest of Amy and me. I'm sure you can do better than that. You're a friend and you're allowed to feel at home here. But... well just behave.

3. You don't just get my girlfriend pregnant. Ejaculating in Amy can have real, significant consequences. This is something the three of you need to discuss. (You're also not sure yet if you'd really be willing to raise a child that isn't yours.)

4. Have fun. As long as Amy likes it, you can do it.

5. Show me how to make a profile on futa-world.

Note: This route here will be an alternative to alex122's full-on sissy-cuck route. While I find a little humiliation here and there okay, I'm personally not a fan of the protagonist (you) being treated like a doormat and acting like one. If Amy is to be impregnated by Monica, it should be with your blessing. Besides, you want to be there when your child is conceived and not in some Doghouse, don't you?