Divorce or not

baza this is true. A divorce just accelerates the division of assets. If you stay together, you will divide them as you spend them over the term of your marriage. If you end your marriage, you just split the assets (and the debts) immediately.

Everyone should remember that in a marriage, YOU NEVER own everything yourself. Marriage is an economic partnership as much as anything. As we all know, marriage ain't just about sex for sure!

Given your past affair, if you go the open marriage route, it may be prudent to mention it in texts or emails and make sure her consent is clear.
If you end up in divorce, it's got to be made clear that your character is unconventional, but not shady. This isn't supposed to affect divorce proceedings, but you do have kids and it'd be good for your wife and you to be on equally unconventional lifestyle footing rather than your activities being painted as conventionally dishonest.

The open marriage allows for an intact home and that new home may be markedly better once you're no longer intimately "trapped". Once I'd decided to date, it was much easier to treat my wife with utmost courtesy and kindness. 
Talking with her therapist (unrelated disaster) inspired a reset that's undermined my dating intentions (which pleases us both). While I was pursuing though, I was seeking out women in open marriages exclusively because they already had the roommate they wanted. (or a primary lover, I never pried.) While Kathy was pleased I picked up our minor check for coffee and donuts, she seemed ready to pay some of the time. The expense should be only slightly higher than having lunches with male platonic friends, if you find someone like Kathy.

If a woman is gold-digging or clingy, you go back to the dating site and find someone more comfortable in their marriage. As Saarinista mentioned, time is often the commodity in least supply. Married women should be largely occupied with the same things you are. They want to make time for the same reasons you do. Lots of online resources are out there for open marriage advice. Multiamory and Polyamory Weekly are podcasts that address specific issues that arise in terms of time-management and jealousy.  Ignore Multiamory's dreadful intro music and mission statement that makes them sound like lizard lounge swingers. They do deep dive relationship research.

Could also divorce, and just not move out. It'll be unusual women that accept that, but it might be cleaner. Basement apartment with separate entrance?

fish, I hope you discussed the nature of your inheritance with the lawyer. In many jurisdictions, inheritance is not subject to the 50/50 asset split unless it’s been moved into a joint account at some point. Because the other side of the coin is that you may end up paying a large alimony for a long while; you might use that inheritance as a negotiating point.

So... I NEED MORE ADVICE!!

My wife started talking about holidays and parents staying yesterday. I said that's not going to happen if we are divorcing. She looked shocked. It was as if she had completely forgotten our conversations earlier in the week, and life was going on exactly as normal. To my understanding we had said that we were divorcing (my decision) and I had given her the only other option of an open relationship.

We talked again. I really think that she was hoping that talk of divorce would just go away like it always has in the past.

She tried to argue again. Then she quickly changed and said it was all her fault and that she needed to be fixed and would see someone not just for counselling but to get psychosexual therapy, and that all her friends have sex once or twice a week (having previously explained to me how none of her friends have sex any more and I'm selfish for suggesting that we should be) and she knows that we are unusual. I asked what I had done wrong, she said nothing and that I was perfect.

I'm really not sure what is going on here, it's either:

1) She has tried the tactic of getting very angry with me, her first response, which included a character assassination for 20 minutes calling me a bully, a narcissist and saying that I didn't care about her. That failed so she tried the ignore the situation and it will go away tactic. That failed, so she tried a quick bit of getting angry again which didn't seem to be working, now we are on to the very passive approach promising to get help, taking all the blame, approach. She has told me she is going to get fixed because it buys her time and is open ended with no immediate obligation on her part, she could spend months on even just finding the right therapist to start with.

2) She has genuinely realised that sex is important and wants to get help to save the relationship.

It feels like a game and I am being played. She has a lot to lose by divorcing: a nice comfy family home, doctor for a husband, I'm fit and well and look after her, a bank account to dip into, plenty of security.

This is a very clever move on her part. It's open ended she could take years getting therapy with no guarantee of anything but it proves how committed she is to saving the marriage and how much she cares about my needs. If I press ahead with divorce I would be evil if she is being so 'honest' and taking all the blame and making steps to fix it.

****What the hell do I do??

DryCreek - my solicitor said that she would get half of everything including any savings wherever they came from after a 19 year marriage, also there is no such thing as an automatic right to alimony in the UK, and advised I don't offer it or discuss it.

fish- something similar happened to me when I asked for a divorce. He was in denial for months- planning family activities and going on with life as if I had not been continually saying I wanted out. When he couldn’t pretend anymore, he had a brief period of “sorrow” over not realizing how much his actions (or inaction) affected me. The biggest difference is that he was honest with me about “not being cut out for therapy”. When I stood firm with my decision and he finally accepted it, he moved forward with the separation surprisingly quickly.

I believe this is another delay tactic for your wife. I wonder how she would react if you stuck to your guns and told her that her attempts at seeking therapy were too little, too late?

Thanks everyone. This forum really is the biggest help ever!

greatcoastal thanks for the links. Reading some of those almost made me cry. I have known for a long time that my wife has BDP (rather than NPD), or at least most of the characteristics, although not a formal diagnosis just my observations. I thought that I knew a lot about it but some of the information was new to me: particularly the article on argument styles, I thought the author must have been watching us argue!! It explains why I come out of an argument wondering what just hit me with my head spinning. And why we never seem to actually discuss the issue she originally brought up, but everything else she is angry with me about spanning the last 20 years..... again!

itme sounds like your ex was BPD as well??

DryCreek yes when I have mentioned divorce in the past she suddenly got interested in sex, once or twice maximum just to make me change my mind. It is a predictable pattern. She has now totally and completely lost interest in sex so it's a promise to see a therapist. Realistically it is just a stalling tactic and nothing else.

Our eldest cat has got really ill over the last few days and I think she is going to die very soon, she is 18 so she is allowed to call it a day. A bit of a break from thinking about marriage issues until she says goodbye to us.