It is very sensible to explore your options, and should you need to proceed I'm sure your friend will be able to suggest the right solicitor for your needs (which won't be her unless she is a divorce specialist).
From your earlier post:
"Had a good long think last night. He was at work this morning and I’ve texted that if he goes to this conference at the end the month with her then he should stay somewhere else for a while when he comes back. He hasn’t responded yet but he has read it."
So, his response is "he will see what he can do about backing out of the conference". And of course we all expect him to now say it's not possible, his employer expects him to go, yadda yadda yadda. Although, to be honest, it's almost immaterial now whether he goes or not, because his 'I'll see what I can do' makes it clear that you are still at the bottom of his priorities.
'I'll see what I can do' is in the same line as his "that that’s just how it is and he can’t help feeling like he does" - making himself out to have no agency, no say in the matter or what he does and what he feels. It's as if he has this romantic notion of himself, helpless, buffeted by the waves of uncontrollable emotion and harried by the demands of a pitiless boss. Which is all nonsense of course, because he chose to have his ego stroked by this relationship in exactly the same way he chose to volunteer to go to this conference. (And I must admit, the theory put forward by other Mumsnetters that this conference doesn't even exist is indeed possible.)
So, if he 'sees what he can do' and then claims the answer is 'nothing' and he HAS to go to this 'conference' - then he also HAS to stay somewhere else on his return. No ifs or buts. If he claims he can get out of it and doesn't go to 'wherever' - I'm still not sure I'd want him in the house, where he will undoubtedly droop around the place sighing at the unfairness of it all like a lovelorn teen.
But, focus on yourself and not him - get advice from your friend and consider your next move. ((hug))