I agree with Casper, back off a little bit. If he is just a fling or whatever then let him go and let him find the other chick more interesting. If you are married then it shouldn't matter who this "other dude" finds more interesting, you already have someone who is 100% interested in you!

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Would you like more sex with that?

I wouldn't recommend sex, drugs or insanity for everyone, but they've always worked for me.