You made the right decision deciding to post. There are a lot of people here who know what you're going through and are willing to help. I wish we could encourage folks new members to start sharing and getting advice, but a lot will wait for months before posting and that delays their progress.
So you're 51 and she's 42, married 15 years, with D10 and S12. How long did you date / know each other before getting married? Did either of you have significant relationships before each other? What are each of your families like, specifically your parents' marriages?
If she already consulted an attorney things are very serious, so it's crucial you consulted one as well. I'm sure your L would've covered where you stand on these major points:
*Custody - Do not settle for anything less than 50/50. *Child Support - Who makes more money? Hopefully L gave you a picture of what that will look like. *Assets - If you married at 36 did you have any significant pre marital assets, and do you live in an Equitable or Equal Distribution state? *Spousal Support - Same comment as child support. There are calculators for both if your L didn't run numbers for you.
IF there are better deals to be had in the D, usually they come quickly. The longer it draws out the less likely W will feel guilt and offer generously to move on. You probably aren't ready for this - many aren't - but if you can get a better deal you may want to make it easy for her to sign off on the dotted line. I AM NOT one to promote divorce, and this is maybe the first time I've said this to someone here, but you can always reconcile after you lock in favorable terms.
10 years without sex is a LONG time. Correct me if I'm wrong, but assuming you wanted more but she shut down? Why were you OK with that? Did it cause you to feel resentment? How did you deal with those feelings?
You also say "I’ve heard she wasn’t happy off and on for the entire marriage". The entire marriage? If true, that's very telling.
You do seem a bit more practical and even-keeled than most, maybe because of the two above comments?
Cut out ANY negativity cold-turkey as a 180. Not convinced that's the single issue which is going to change things, but doesn't hurt to implement it - and probably best for any of your relationships (friends, family, W...etc) anyway.
Sorry to ask, but...any signs of an affair? Fair warning - there almost always is one.
Me:39 Ex-W:37 M:7 T: 9 S:6 D:3 BD/IHS/Confirm EA/PA: Feb '20 OM1 affair ends: May '20 W/OM2 & moves out: June-July '20 W files for D: Jul20 OM2 confirmed: 9/2020 Divorced: May '21