Her pussy.

You figure she won't care too much and you release your seed into her pussy.

"Ohhh! Oh Nick! It's a good thing I'm on the pill."

"Don't you find it odd that you just taught us about safe sex and we just had unsafe sex?"

"Had? Oh no, we aren't done yet."

She pulls your cock out and turns around. She then pushes you into her chair and straddles your still hard cock.

"Ready for round two?"

She doesn't give you much chance to answer as she starts gyrating her hips around your cock.