I don’t know when this separation was, but it seems recent to me if he was dumb enough to keep all those messages. I don’t thin’ you should feel guilty for “snooping,” is it snooping if you’ve been together for 12 years?
Why did you get back together with him? Why are you in a relationship where you don’t trust him, and he doesn’t give you the intimacy you crave? Is it for the kids? Seeing you accept the bare minimum and stay unhappy for years is not going to teach your children good things about relationships.
I think counseling is probably a great idea, even if it’s just for you.