TREUETEST with my stepsister's boyfriend!

Imagine you've only been with your girlfriend for a pair of months and her big stepsister is an incredibly hot woman who you're constantly having sex with! Unfortunately, things aren't going well sexually with your partner, so the conversation with her stepsister came at just the right time - because she wants to seduce you and show you that things can be different in bed! Would you weaken and cheat on your girlfriend or stand firm and be loyal to her?