Imagine your girl sitting down with her new lover while you sit in the corner and watch. You know it shouldn't but it arouses you so much. Give me 50 strokes
Now imagine how wet she would be from the excitement of a new cock. A bigger cock. She is so beautiful and deserves to be fucked in a way that you know you could never offer her. Start rubbing just the sweet spot through those panties with small circular motions.
The thought alone of what comes next really drives you wild! The thought of seeing your girl naked and exposed in front of another man makes your dick so hard. You know how excited he must be to conquer something he has never had. Your girl excited to feel the rush of a new touch. Keep rubbing the sweet spot.