I think what you had when you got married matters if you had assets you brought to the marriage, as they would be counted as yours. So this is where it is important that you both ask your respective banks to provide statements from when you got married. You also need a valuation of your pensions which your employer should provide. Basically the solicitor will give you a sheet with every possible asset or debt possible at the start and end of the marriage and go from there. what happened in between only matters really if one party has got savings put away during the marriage and the other has not (eg in my case from paying all the children costs despite us earning the same)
I ended up having to file in court and ask for x amount, based on what I thought it should be (as he stalled at every point). I think that x was less than it should have been but the child arrangements part was so hostile and difficult, making sure the DC were okay was my priority (which chimes with what Phleghm says). The money went straight to the legal fees. So if you can agree via mediation, so much the better. You can always ask for a % higher than 50/50 which he may agree to, but the law works on the presumption of 50/50.
I suppose one thing is if you can get the financial settlement out of the way and keep the house, and you have your job, then you do have the independence and autonomy and you won’t be seen as the default to provide care for him should he need it (sorry that sounds really mean of me, but now I just think well, it is the new girlfriend’s job to be the support person). My house also needs work (too busy earning the money right now to focus on that and paying various other costs), but it is mine. It’s a case of doing what you can when you can and finding joy in what you have. Plus you might want to move in a few years time, you don’t know. One thing at a time. If the finances are settled, you have more choices.
Also, our separation took several years to resolve (and we are not divorced yet) and that was with solicitors involved. This glacial pace is not the norm, my ex is just a bit of the controlling type (he stopped this when he met someone new, but by that point, I gave up with it). But it is a process which can take time.
28 years of marriage is a long time and there will also be a lot to unpack emotionally. I would take care to ensure you have real life support and time for yourself to process this.
thank you for your good wishes too. I hope you find a way through this which works for you.