In hindsight, my friend should have seen the signs. The wife became super rude, disrespectful, always travelling and had lots of money whose source could not be accounted for. And then, like all cheating partners are wont to do, she became careless.
She had become so secretive with her phone, guarding it more than superpowers hide their nuclear codes. My friend did what any insecure man would do, used a software to intercept messages and calls on his wife's phone.