Here's the deal. I text some women friends - just joking shit. But, I text guys the same shit. I'm an equal opportunity texter. If my wife questions what I'm sending, I don't hesitate to show it to her. My thoughts - and exactly what I have told my wife - is that if I am texting someone and I can't let her read what I wrote, I shouldn't be sending it and it's probably inappropriate.
Sorry to hear about all this shit, but it's not worth the heartache it will cause - get out of the relationship now. Don't give her the chance to explain, just stop communicating with her.