Advance apologies for temporarily taking this thread off on a parents of transitioners tangent rather than keeping it on topic for partners, I promise not to do it for long!
As a stepmum to an ROGD nearly-17 year old and a three-times-married woman with multiple mother-in-laws I have a potentially useful combo of lived experiences (😬)
(Plus, I’m a major Tinsel Angel fan and aspiring trans widow ally 😍)
Firstly, there are increasing numbers of parents of adult children joining the gender skeptical parent groups - thousands of ROGD teens are now young adults anyway and once a child is legally an adult a parent has very little sway so there isn’t much difference between the experiences of say, a parent of a 25 year old and the parent of a 45 year old (except for grandchildren being more likely).
I would definitely encourage parents of transitioning children of any age to make contact with these groups - the more parents of adults who make contact, the more likely it is that tailored peer support will come into existence.
In psychosocial terms an individual’s transition affects the entire family ‘system’ (something that trans widows will attest to).
Perhaps with some time and space your soon to be ex daughter in law will be in a
position where she is willing to think again re: contact with you @Cholumenosoapy?
Obvs I don’t know what your relationship has been like during the marriage but if I were in a similar situation I would send my imaginary STBXDIL a good old fashioned letter (not an email or text) stating what you have told us - that you understand why their marriage is ending, that you accept her decision to prioritise the well-being of her children, that you are disappointed in your son’s actions and that you are mindful of how difficult her position is.
If you are able to offer practical support (help with childcare or finances etc) or emotional support, offer it, or ask for permission to send the kids Xmas and birthday cards/gifts via her but (and I cannot stress this enough) don’t make her or the kids any promises you can’t keep (her STBX has already done quite enough of that thank you very much!)
And then BACK RIGHT OFF (with the assurance that your door will still be open to her and/or the kids even if it takes several years for her to want to come knock on it).
And yes, protect yourself, your son is 45 - he’s of the age where the parent/child relationship naturally and gradually should flip until he is the one looking out for his mum’s well-being, he shouldn’t be draining her of her emotional energy.
I’m glad you have found a counsellor who is able to support YOU and isn’t unduly influenced by the transactivism that has been targeting this professional arena.
Lastly, If relevant, I would seriously consider writing/rewriting your will.
Late life male transitioners burn through money at a rate akin to a gambling addict, clothes, shoes, wigs (& hair transplants) make up, multiple cosmetic surgeries (often combined with a foreign holiday), nights out, even a new, ‘girly’ car - it’s like a classic midlife, sports-car-and-shagging-the-secretary crisis but with infinitely more stuff to spaff the family resources on.
If you are likely to leave even a modest inheritance then reorganising your will to leave all (or most) of what would’ve been your son’s directly to his children would be a simple way to counteract some of the negative financial impact that a typical, late life transitioning father has on his children.
Just make the changes privately with your solicitor - no need for endless family dramas talking about it - when it becomes relevant you’ll already be gone and your former DIL and grandchildren will be left with the knowledge that you meant what you said in your letter re: prioritising the long-term well-being of your grandchildren over the desires of your son.
I’m sorry this is happening to you but you are not alone and hopefully you will be able to make contact with others in a similar position.
Genspect has a long list of orgs on their link page (will go fetch it and add to subsequent post as MN has an annoying habit of reloading and wiping an in-progress comment - we desperately need a ‘save draft’ function!)