I've been in EXACTLY your seat. I've seen those messages, pictures, etc., It feels overwhelming at the moment, I know how you feel!
In our culture cheating is seen as the worst nightmare that can happen to a marriage. I kind of look at it a little different though. I think cheating is a symptom of other problems. And those problems don't even have to be huge either! People just have a tendency to act on their emotions. Emotions are sooo unreliable, so fleeting.
Please take a deep breath and take care of yourself. I'm praying for you!!