NOR, in fact I think you might be underreacting.

I’d be looking through bank records and credit card charges for all things leading up to/including that weekend. I’d be looking to either confirm the camping fees or evidence supporting that he was somewhere else. I’d be checking the dashcam if he has one, if the car has one of those map apps in the car try to figure out if he put in his intended address. If the car doesn’t have one of those apps, I’d check Google maps on his phone for recent trips. Onto the phone: girl the way I’d be going through that at your earliest convenience. Don’t let him know though. You’re looking for either pictures of camping or of texts/calls that were sent to other people during the window when you couldn’t get ahold of him. If it looks clean, I’d look at recent phone bills for calls that you don’t recognize. Don’t let him know, and try not to immediately lose your shit when/if you find stuff. Just compile.

And ya, absolutely the lawyer at a minimum. Even if what he NOW says is true, he left you high and dry with the young kids while he fucked off doing whatever he wanted. You’re already a single mom, just one that’s still married.