Dear @Suffolkcatlady I am so sorry, your life sounds pretty horrendous right now, and as if it has been for quite a long time. Without anywhere near the provocations you are, and have been suffering from, I also had times while my children were growing, up that if I hadn't held in my mind the place that I would escape to if everything became just too unbearable, I am not sure that I would still be here today.
So please don't think you are alone in these sort of feelings, and please don't feel that you are bad for feeling them, they are very understandable human emotions brought on by bloody unfair circumstances. I hesitate to give you any advice moving forward (except like others have, to see your GP and tell her what you have told us), but if I were you, in the circumstances that you have already told us about, I would take DD2 on that city break, then when back home I would tell all of my family that I need a break on my own "to recharge my batteries" I would tell them that I am not going to say where I am going as I need some "me time", without any interruptions.
If I had some one outside the family that I could really trust (like a best friend), I would give her a number that she could call me on, and ask my family to contact her - but only in the case of dire emergenies. Seperate to my children, I would tell my husband that I really need this break, and that it holds the only chance of our marriage surviving. That I am really sorry to leave on a cliff edge, but that I just don't know anything more myself at the moment.
However, if I felt that neither my children nor my husband could just accept that, and that they would cross question me, and/or get very emotional, then I would go when they weren't there, leaving a short note saying I needed a break, and they would get a written explanation of sorts tomorrow - maybe by snail mail that I had posted that day. The explicatory letter would just say the things I would have told them face to face if I could have faced it.
@Suffolkcatlady I don't think you even need to think about whether you want to divorce your husband yet (although if you already know that you do, it does not have to happen before you have your break). Your "break" can be for however long you initially would like to set if for, but if you want to be fair to both yourself and your family, I think that two weeks could be a good compromise. I hope that after a fortnight you would have a good idea about whether this needed to become a long term solution for you involving all of your family, or if you "just" want a permanent separation and then divorce, from your husband.
Again, in similar circumstances, I think that I would take a fortnight away, at first to gather my thoughts, then when I got back I would see my GP, and get whatever help I could from her, which may or may not include medication at that time, and if I still wasn't sure about my love for my husband, I might seek marriage counselling for us together, or just personal counselling to help me through this very difficult time.
If you have managed to wade through this catlady, then I apologise for both it's length, and the time it has taken me to type it - I started this at about 3.30pm this afternoon, but then had to see to a lot of other things, it is now about 10.18pm so many things may have happened to your post in the meantime. I feel sure that you will get through this, and come out both happier and stronger in the end, but please remember that you have people here (including me) who are ready, willing and happy to listen to you, encourage you in doing what is right for you, and support you in your choices. Good luck OP 💐