Separation timing when older children are still living at home

[DelightfullySoSo]

I need insights and experiences especially from those with older kids at home at the start of separation process to help me make wise decisions on timing.
My situation: Married nearly 25 years. DCs are 16 and 20. The 20yo plans to finish their last year at uni here at home (we barely see them and they drive etc) which I’m happy about as I always wanted my DCs to complete their education debt free (we’re in Scotland so have a head start tbf).
The 16yo is not sure of their next step so in theory could be at home for another 4-5 years.
H and I have been on a rollercoaster of volatility / slow separation but are in a strange season of ‘hanging on but neither is sure we want to stay married’.
He has complex mental health issues (autism+childhood trauma+seasonal depression) which are getting more concentrated in his attitudes and behaviour and difficult to live with as he ages. (He would agree).
I do love him and feel (probably unhealthily) bonded to him but - frankly - don’t want to live with him. I cannot see a happy future for me with us living together (he’s able to just live all but parallel lives but I find it very inhibiting). I suggested living apart but staying together and he dismissed it outright. He feels we are only husband and wife if we share a house. Problem is, I need a home….
I’m turning over every stone to try absolutely everything to make it work. Solo and couples counselling, pastoral counsel from our minister, changed my HRT to rule out any imbalance on my part, reading all the books and listening to all the podcasts, I even took 6 weeks off work just to focus on my mental wellbeing to make sure it’s not me being unreasonable .. but he won’t even see a GP and explore anti-depressants because he’s “fine”. He has categorically said ‘take me as I am or leave the marriage’. And he will not leave the house.
So things are currently amicable (until his next meltdown- the most recent of which had him screaming and swearing at me demanding I let him out of the car.. whilst I was driving on the motorway).
If I over-function in the relationship, do the emotional heavy lifting and ‘manage’ the marriage, and keep myself healthy and busy, then day to day life under the roof is okay - but things can change in a second and I never know when.
I keep ruminating on 3 options.

1. I wait for the kids exams to finish in a few weeks and then leave (with my youngest) and either leave 20yo and H to the house until it can be sold when 20yo finishes uni next May. This feels like the ‘nuclear’ option to me as my 16yo has a final year of school and I would be splitting the family up.
2. I wait longer - until next May - when both DCs finish their final years and then we split and sell up. This feels like the most natural junction but the relationship with H makes me anxious all the time and I am not wild about compromising on my peace for yet another year… (but then, it’s one year after 25 so perhaps the path of least resistance as my DCs would be least affected which is extremely important to me).
3. I keep going with my efforts to understand and navigate his behaviours (he’s not all bad by any means, it’s just not a relationship I ever feel relaxed in and he has told me he doesn’t like being married but likes me..(?) and just see how we go over the ext few years. This feels like the higher risk option as I’m about to turn 50 and drifting on and on is what I’ve done for 5 years already for the sake of keeping the family unit together.. when I’m fantasising on a daily basis now of having my own home and life and young enough to recover fully from a divorce I would hope.

[We are very recently mortgage free thankfully and earn about the same so financial separation will obviously hit us both by separating but not in devastating ways, which I am very grateful for.]

I can’t see any other ways forward and I’m in such a mental and emotional muddle. I hope someone is out there with some suggestions for me..

I think the answer to this question partly is about how aware the 16 year old (and to a lesser extent the 20 year old) is of how bad it is?

Parents separating in the last couple of years at school with pressure of exams etc is pretty rough. I am not sure exactly how the Scottish exam system works, and when key exams are, but in England I would try and hang on that last year til major exams are over.
BUT if the kids are pretty aware, then they may well cheer you on in separating.

I think I would be honest with your kids, talk to them and say this is not going to last long term, dad and I are going to split at some point. You may find your 16 year old says - please do it now.

By the way option 3 is not really an option, it is like being buried alive. Don't do that to yourself.

The other comment I would make is that kids still need a base, even when post uni, so you do need to be clear that they can always come home, and have a bed/sofabed they can use. It si relaly an emotional base for some.

Thank you. They’re both fully aware and struggle at times themselves with his behaviours. There was a particularly triggering argument a couple of months ago (serious enough that I saw solicitors, told my boss etc) and the 16yo did say they were braced to leave with me. The 20yo is focused on exams and preparing for leaving home in the next year so they’re pragmatic and say they completely understand I need to find peace, even happiness longer term. He has a gf and is spending more and more time at her/her parents house where they seem to be a welcoming and hospitable emotional base, as you say. It makes me sad because I know that with H’s ways I don’t think either of our DCs would rush to come back unless they had to. It’s not an unhappy house (present circumstance aside) but it’s quiet and ‘stale’ and awkward. Neither brings many friends back and it breaks my heart because H is happy with that.. whereas I foresee grand parenting as an absolute joy and H views it as a bind/extra responsibility he would be in no rush to accommodate. So the long view is one that makes my heart sad too because I am those kids’ home - they have told me they love my presence and feel loved and safe but can see the marriage is grinding me down and consuming me. They love their Dad of course but it’s hard for them. I want a future I’m excited about.

“He” being 20 yo son!

First option. Any other one leaves you unhappy for shorter or longer times. Living eith someone so unstable for another year would be a killer. Can you tell the 20 year old they can come too? Or have a bedroom for them in your new place? Your 16 year old will be fine if they're sitting Highers this year. They also might be able to travel to school next year for sixth year.