My girlfriend gives a handjob and swallows my cum while my stepdaughter watches

I've always had a thing for my girlfriend's stepdaughter. She's not my daughter, but there's something about her that's just irresistible. When I'm home alone with her, I can't help but fantasize about what it would be like to be with her. But, of course, I know that's not an option. So, I settle for the next best thing - my girlfriend. She's always been a great lover, but today she went above and beyond. She gave me a handjob that had me moaning in pleasure. And when she finished, she eagerly took my cum in her mouth, swallowing every last drop. But the real twist was that our little show was being watched by her stepdad's daughter. She was hiding behind the door, watching us with a mix of shock and arousal in her eyes. It was a sight I won't forget anytime soon.