Yes catperson, you do need honesty in a marriage, but it should be freely offered. Confrontation and snooping aren't going to accomplish anything other than pushing your partner further away.
F4ML, read Sandi's Rules - these can be found in the Newcomers section. Among the other rules it say "do not spy on spouse by checking emails, phone bills, etc". Hopefully a vet will come along and give you advice as well, but I'd certainly start by not snooping. You're not going to feel any better by doing so.
There IS a "third way" here. Simply ASSUME THAT HE IS (having at LEAST an emotional affair), and plan and behave accordingly. The chances are extremely high that he is, based on what you've told us here.
I'm with cat -- I'd rather have the solid proof, and plan my life accordingly -- but if you think you can't handle what's necessary to get it, then merely assume there is infidelity here, and proceed accordingly.
