Finally, after slowly teasing you until the pre-cum is flowing strongly and you are moaning with horniness, she gets up and says:
"Well, I guess I'll have to use some other ideas... I'll be back in a bit..."
You feel sad when she leaves you alone, trapped in the humbler. But more than feeling sad, you feel extremely horny and ache for release. Your cock drools pre-cum as it softens, and you feel embarrassed and humiliated at being in this situation with your wife's sister...