Oh dear. You have my sympathies. You have obviously had a long marriage, you still love her and feel the loss keenly.
From what you say, your options are
1. Agree to a divorce by consent ; or
2. Not agree, in which case she could divorce you for UB or wait another 8 months when she won't need your consent.
I am afraid I think your suspicions that he has found someone may be well founded.
Why is she doing this now ? She's been separated for almost five years. She
could simply choose to remain that way, but doesn't. The obvious reason why she wants to do it now is because she has found someone else and wants to marry this person.
Unfortunately you won't be able to stop her
divorcing you if she's hell bent on it.
After 5 years it's more or less automatic.
Whichever method is chosen is very unlikely to affect the issue of financial provision, but if she has indeed found someone else, then that could make your potential burden lighter for a number of reasons. if she is living with him it
means her housing needs are satisfied, and
that could weaken her case for a sale. After such a long marriage she us going to get something, that's inevitable, but it's a little hard to advise without knowing your respective circumstances.
It is naturally emotionally hurtful if my suspicions are well founded. Sooner or later you will both have to fill in something called a
form E and that will ask her whether she intends to marry or cohabit, and if she answers Yes, then you know.
I'm sorry if I have got this wrong, but I
sometimes do have to give advice which is not welcome. Good luck. There is a lot of support available on this site.
LMM