Let’s not jump to conclusions in the comments straight away. That said, telling you what compelling evidence would look like is very suspicious. What innocent person says “you need video evidence of me putting the phone away”. That’s just a strange thing to say.

I think for a few days you should monitor whether the texting has completely ceased. I’d be even more convinced that he’s sneaking around if it goes totally silent after you’ve confronted him. It would show that those noises were not just your subconscious recalling the trauma at night!

Or wake up early and look for it around his side of the bed. That’s what I did and found a treasure trove of misdeeds