Thanks @Highlighta
Another really supportive post, how unmumsnetty! 
Yes, it’s the broken trust. And the lying.
We had three children in quick succession, and I got made redundant and had to work long hours retraining not long after.
He was working shifts.
We never saw each other and when we did we were just arguing - about the mess in the house, the kids, money. No sex life.
This woman offered him some attention when I was giving him none.
He swears it didn’t go beyond messages / sexting, swears they never met up. But he was lying a lot when I found out, and had to drag every bit of the story out of him. He says because he didn’t want to hurt me and was so terrified of losing me and the kids.
you are correct in what you say about the divorce process. That terrifies me too. And the fact that no matter which way we cut it, we can’t afford two houses.
I won’t hijack the thread anymore, I know this isn’t intended for me. I was reading with interest and felt compelled the post and am grateful for the well measured replies I’ve had.