Scene idea: you’re at a sex club with your girlfriend. You’re in a room where a couple is having sex in a bed with others watching. Your girlfriend tells you that when one couple finishes, any couple can go put on a show for the crowd. You shake your hands to tell her you aren’t interested. After watching the couple for a few minutes, your girlfriend tells you how horny it is making her. She pulls out your cock and starts giving you a bj/ hand job. The couple finishes and leaves. Your girlfriend tells you the two of you would put on a great show. She gets up and walks to the bed. Of course, you follow. You creampie your girlfriend and the onlookers applaud. End scene.
The scene could also be a threesome with your girlfriend calling one of the lookers up to the bed with you.