Overthinking it

I've been with my husband a total of five years, he has always proved to be loyal. I recently found a message sent from an account of his to a girl nothing too bad it just said good morning beautiful. She replied but he never opened her reply. I found it a month after it was sent, so he never opened it for a month. He said someone hacked his account and I was having trouble believing. I messaged the girl and she said they were just friends, shortly after I messaged her tho someone tried logging into his account but it failed. I saw it with my eyes he didn't tell me. It was from a different state and place. So I believe his account really got hacked, and he has even proven his loyalty by blocking said person with me asking and even going farther and deleting other girls from his page that I've know and he knew just to make me comfortable. My issue is is that, everyone around me says it sounds like he wouldn't cheat and I believe them, but Im pregnant and severely depressed and just can't get the doubts and anxiety out of my head. I believe him I do but it's like my mind wants to self destruct