I'm in a relationship with a man who is still (technically) married - he and his wife separated nearly a year ago, we've been together for several months (we didn't meet til more than 6 months after his separation so I was never the OW or anything).
It was his ExW initially who wanted to separate and asked him to move out, as she was unhappy, felt they had grown apart etc. They tried Relate first, moved house, changed lifestyle etc but it didn't help.
A few months later (before he met me) he put the wheels in motion for the divorce, and sent her the various docs she needs to sign/discuss with her solicitor (sorry, I don't know the legal ins and outs) and basically she hasnt done anything with them. Every time he asks her there seems to be a different excuse. He can't understand why - she doesn't know about me specifically (neither of us feel comfortable being 'open' about our relationship until the divorce is underway and he at least has his decree nisi) so I don't think it's anything to do with that. She doesn't show any sign of wanting to get back with him either so I really don't get it, especially as she was the one who instigated the split in the first place.