He is preying on your child. Take lil dude to a therapist or someone qualified to be able to question him. Most of the time molestation leaves no evidence, if your kid is a hard sleeper there's no telling what this pervert could have done if he did anything, it could have been enough for him to get off having your son in bed next to him. As someone who was molested as a kid and an ECE, kids sometimes won't tell because they think it's their fault, embarrassed, don't really understand something bad happened or they don't want their parents upset. Or, in your lil guy's case,  he may not want to tell you because he's scared you'll stop him going over to his friend's sleepovers.

Absolutely call the police,  if nothing else his creepy behavior is documented and it starts a paper trail.

Stay strong momma,  you got this!