YTA

The Wife cheated, however the healthy way to handle that is to discuss why- especially if it was a one time thing five years ago. Hell we don't even know if the digital blunder was you found a 5 year old drunk night out pic. But the way you make it sound like some switch was flipped is disgusting. And the child scenario makes me think that you clearly did something to push her to that early on and unless we know why she cheated or if she was even aware of it or whether it was intentional. Especially after 5 years.

The Child has called you dad for so long and you and a bond for 5+ years and your not only completely fine with walking away from them but don't even want to speak to them.

How anyone can say that you are not the asshole when your walking out on the child you called yours for so long- it's revolting.

Cheating's common and you should grow the fuck up.

If this was 7 months in, sure go ahead. Attachment and damage is minimal. But 7 years, your a monster. Is it