Gently, these are all feelings that stem from thoughts, which are springing from ideas, and stories you are telling yourself.
Your feelings are all valid, and we all feel how we feel, but it's very useful to examine the underlying thoughts and beliefs that are causing us to feel those feelings. Try to pull them apart a bit. Some of them may be useful - recognising that you always wanted a loving and happy marriage, and that you maybe grieving for that, for example. Some may not be - extrapolating into the future when you really just can't know how things will change, for example.
It's worth looking closer at your thoughts and considering them in more depth.
'I can’t imagine having the time now to re build, start over, let alone have a loving and happy marriage which I’ve always wanted. If this happened when I was 25 I might feel differently but at 38 it seems so much had already been laid out for me now that I can’t change. Single and alone with a very small child and huge money and job worries alongside loneliness. It doesn’t seem as fixable at 38 as it would at 28.'
I hope that makes it a bit clearer? You are creating an idea of how things 'seem'.
Can I suggest a useful book?
https://www.goodreads.com/en/book/show/46674
Is slightly dull, but I found it useful for helping to identity 'thought habits', like catastrophisation, fortune telling, black-and-white thinking, etc, that all can contribute to low mood, depression, and generally feeling like shite.
Also 'the work' by Byron Katie. Which boils down to asking yourself:
Is that true?
How do you know?
And of course, therapy or counselling may be useful, as might be talking to friends and family. And/or mindfulness.
A useful resource:
https://franticworld.com/