@Cuppacakey, you know what you saw and your observations have proved correct.
P’s behavior after being caught out just reeks of guilt. He provided zero empathy, transparency or reassurance. Instead, he pulled out all the stops to control the narrative and bully you into backing off: name-calling, threats, and blocking transparency on his phone and FB. His priority was protecting his crush and their relationship.
They’ve clearly been simmering since being together in the car months ago, or possibly before that. His phone has been accompanying him to the shower, and I assume this is an unusual recent behavior. At the very least, they’ve been messaging, which is highly inappropriate.
He figured he could get some snaps of her dancing, using your young DD as cover. He assumed you’d be clueless, but his singling her out for photos and affectionate gestures, plus her awkwardness with you/laser focusing on him, were dead giveaways. He’s kicking himself that he blew his subterfuge.
Keep posting, @Cuppacakey. We’re here to support you. If it would help, go through all the comments and pull those that might be useful to you as you organize your thoughts and read him the riot act.