confront him or leave it alone.

So I've been seeing this guy for a couple of months. Everything has been going good, I've met his kids and his mom. We've already talked bout moving in together and getting our own place with the kids. Well today he gave me his phone to sign in to Amazon. I noticed he had a notification with 2 hearts which i assumed was a dating app. Well he went downstairs so i looked and he first had a notification from plenty of fish that someone liked him. There then was a second notification that they had a mutual liking so I'm like wtf. I don't know if he just didn't delete the app and still gets notifications or if he's still using it. But idk how to bring it up in conversation or what to do. I don't wanna start a fight because i really like him but if he's still on a dating app i can't be with me so idk what to do.