@Tcof
No, really, it's on the list of why wars are started.
Example (Don't take it personally), you see your wife talking to another man. You don't say anything about it.
Next, you see her kissing that man, yet you still don't say anything. Then finally, she had sex with that dude, and you burst out and call her a 'slut' and various derogatory terms.
So, how could that have stopped before it began? Talk to both of them, try to get in between.
And don't be a Jerry.