Jack is just a normal guy. We the viewers love seeing Jill get swapped because we can self-insert as the guy who gets to fuck Jack's girl, but almost no man wants to see their girl get fucked by another guy. That is cuck behavior. Just the idea of a threesome with your girl and another guy is unthinkable to me. Yuck.
Well the next thing I foresee is Jill getting gangbanged. I mean what's good for the goose...
No offense but Jack is absolutely not a normal guy. He fucks like a dozen different girls a week and yet is an insecure crybaby about Jill doing another dude?
Jack is a normal guy with a not-so-normal career. Very few of us in his position would want their wife to get fucked by another guy no matter how many girls he gets to fuck. It's totally normal to not want to share the mother of your children with other men.