I got a letter through the post and confronted him about it. It is true, he is still married. He split up from his ex in 2004, i know this is true as his (adult) kids have confirmed this. She is not a UK national but is resident in the UK. She has always refused to sign the divorce papers. The only way he can get a divorce is if a bailiff serves papers on her - he tried twice in the past and she just didn't answer the door. Apparently he is trying again this week (no doubt prompted by me finding out).
It is clear to me that he is in no way in a relationship with her however, it's the lying that is getting to me.
A few years ago, I got another anonymous letter claiming something else about him - nothing as major as this - I confronted him at the time, he told me (what I thought) was the truth. I thought about ending the relationship but again, it was something in the long distant past but here is the clincher. I made him promise that he told me the absolute truth about everything. That we had a sort of amnesty whereby anything in his past that was going to come back and bite him or me was brought out into the open. He promised me there was nothing more, absolutely promised me.
And now this.
I can't even look at him now i am so pissed off. Splitting up would be a huge thing - we don't have kids together but have a massive tangle of living relationships, dogs, cars, kids who reside temporarily with us and I'm pissed off about the financial stuff as we have joint accounts at the moment which I imagine if his exw wanted to be super difficult, might be an issue.
Just wanted to get other people's opinions. I haven't been brave enough to tell any of my RL friends.