BF saved and masturbated to almost every girl's pics he ever dated—can he really change?

We’ve been together for 2 years (he's 26, i'm 22). He’s always been my biggest supporter, always there for me during my struggles. He made me feel loved and appreciated. However, while we were dating, he still followed around 5–7 girls he had talked to or went on a date before. I told him six months ago that it bothered me when he liked revealing pics of a girl he met on Tinder (before we were together). He got defensive, called me insecure, and even cried, saying he’d do anything to gain my trust. But I checked—he never messaged anyone inappropriately, just wished two girls happy birthday. After this he liked 2-3 pics showing abs of that girl but not a single random picture. ONLY where her body was showing.

Two weeks ago, I accidentally found he saved revealing photos of girls in his phone. He lied at first and said it was just a “one-time thing.” then confessed: he had a secret porn folder on his phone, secret Instagram for soft porn, used multiple platforms for it, and even saved and masturbated to almost every girl he ever went on a date with. (I’m his first relationship.) In his instagram saves there were also underage girls just dancing ballet and stuff…I told him i even developed ED because of him. He says he'll never forgive himself for causing me so much pain. He admitted he never saw it as an addiction until now. He broke down, saying he’s disgusted with himself and wants to change. He says this was a wake up call for him. He’s doing no fap and claims he has no urge to go back and even if the urge comes he’ll resist.

It hurts because we weren't only lovers. We were best friends sharing EVERYTHING with each other and being our real selves...

We had sex recently, and he didn’t last long—he says it’s because he hasn’t masturbated for a long time.

I want to believe him, but I’m scared this won’t last. Am I being naive to think he can really change?