@Feelinfedup I've now seen your updates. You have clearly reached the point (understandably) where you can't see a future with him - and all I can say in that case is that you will have a horrible time for a while, but there will be better times to come. You have four children who care about you, and nobody can ever take that away from you. You may or may not meet someone else - it's not top priority at the moment. You are your top priority now, and you need to do whatever you can to ease your path out of the marriage.
I had only ever slept with my ex husband, and we had been together 25 years, so I know how you feel on that score. But thinking about sleeping with someone else is right at the bottom of the to-do list now. What you need to do, given that you have decided to take the unknown and scary path (which will, in fact, lead to better things), is put your practical head on and find out what you are legally entitled to. You have been married a long time and have four children. I don't know whether you have worked during your marriage; I can only say what happened to me as a SAHM, but other women who carried on working will be able to advise you as to what might happen if you've worked during your marriage.
For a long term SAHM with (mostly) adult children, I'd guess a 50:50 split of assets and pension, with a 'clean break'. I had a clean break 60:40 in my favour, but my children were younger. I was able to buy a house outright - not the 'forever' house we had before, and which I imagined our grandchildren in - but now that all my children are older, I know that I don't need a huge house. Ex husband has never paid me (or the children) a penny. Do get legal advice specific to your situation, though.
You will get through this, and you will be okay.