I would confront him about it. Sounds to me like he's hiding something. If you don't have trust then you don't have a relationship.
What do I do when my boyfriend who I've been dating for 9 months keeps being shady about his phone (charges it face down, talks weird when certain people call, & gets nervous when I hold his phone)?
If he says nothing when you confront him... I would say don't snoop.... But if it comes to it you might have to. You never know whats going on, and he might be getting himself in trouble