Two words, and probably jointly responsible for more relationship break-ups than anything else.
Followed closely in third place by "money".

Note: If you watch porn make it very clear to the woman that when the camera cuts..... the guy is actually having a break and doesn't do it non-stop for 2 hours ....
Good tip

Been there and done that with all the trust & jealousy mind games. I never question my missus about whether she's being faithful or not, if she was going to she'd do it anyway, and by being a suspicious pest you'll only drive them away in the end anyway.

You gotta have faith in your own abilities to make the other person happy so they don't stray away