My dh says she’s just a really nice person who couldn’t help falling in love and is in unhappy marriage.
Well she didn't love him that much because she dumped him!
She doesn’t seem more attractive than me except in the kind and sympathetic department.
She can't be that kind - she was willing to go and fuck a married man and cheat on her own husband.
Apparently she wanted to break up with dh but stay friends as they were always such good friends before the affair. She wanted to carry on getting projects from him as his company was her main source of income.
This - genuinely - is the root of why she wants to be friends with him. I don't think she gives a crap about your H, but she DOES care about her income being compromised.
She wasn't in love with him - she saw a way of getting a nice ego boost and then when your H turned serious she scarpered. Your H knows this and is now re-writing history because he can't face the truth - which is that he's thrown away his marriage for a woman who wasn't that into him.
See a solicitor, get some good legal advice about your financial position and pensions, and then file for divorce. You are worried about being alone? Darling you are ALREADY on your own - he checked out when he started shagging the OW. You can be lonely in a marriage and it sounds as if you are.
He's too wrapped up in his own misery and selfishness to care about the impact to you, which tells you that this marriage is dead in the water. God willing you've got another 25 years in front of you so make them count.