I'm the first person to come here and say that I don't condone snooping and that having a need to indicates that there's no trust in the relationship already, regardless of what you might find.

But here's the deal; it's done. You snooped. Turns out you were right not to trust him. But does you being wrong change the reality of the situation? Is he any less of a scumbag because you went through his phone? Of course not.

"It's over. You're a piece of shit who can't be trusted." You don't need to overthink the conversation. You don't need to approach this sensitively. You should know that the end game here is that you're ending the relationship. What do you want to work? A relationship where you're constantly disrespected? Respect yourself enough to walk away. Good luck.