Pull Mark with you

You decide to act fast.

"Come with me" - command you to Mark and walk down the stairs.

When you reach living room with a walkway to backdoor to your garden you stop.

"I want you to go with me to our workshop" - say you. "Tell guys you'll be later."

"What for?" - starts asking Mark a minute later but you interrupt him, so he follows you to the yard.

"What're you playing?" - asks Mark when you step into workshop. Here is a bit of dusty but the couch is here and dim light due to tree shadow makes it intimate.

"I want to have sex with you." - rush you after a short thought.

"Jenny, are you OK? I have a girlfriend and you're my buddy's sister... And you've never show me some attention..."

"Well, things changed and now I want to have sex with you."

"Not saying it's a bit strange, saying about sex without single date but as I said I have a girlfriend and I'm not going to cheat on her... Even if I will regret it." - confesses Mark.

Damn, it's going harder that you thought. I would greet such fidelity in a guy... but not now. You have to propose Mark something he would not deny. But what? Money, promise, your sexy photos or what?