Step 1. Get your boyfriend in a position it's hard to get out of. Step 2. Put his cock in your pussy. Step 3. Brag about how many guys you're cheating with while he tries to squirm away.
She didn't want to cheat on you with her best guy friend and she didn't want to get pregnant either so she figured this was fine. It didn't go in her so that's ok right?
Your monogamous wife has a slutty BFF who got her drunk and gave her drugs. Now a random guy from the bar is about to ejaculate inside the mother of your children.