I went through this with my husband. Somewhat different circumstances, but I know some of what you are feeling.

I am assuming you believe this stranger that called you. Now, you have to do what is right for you. A long talk with your husband is definitely in order. I'd show/tell him what "evidence" you've found and don't be afraid to tell him that you don't believe him when/if he denies it.

PM anytime. I've been where you are. It's a very lonely place.