Sorry to hear you feel rubbish OP 
But, from a different perspective..
I have friends who are the same age/ older than you, and who are still looking for Mr Right, and who have no children. You have brought up three children- surely there is an achievement in that? AND there is no reason why you won't meet anyone else. I would bet that you have met men, they just haven't been what you were looking for- good for you: there is a a sense of self-worth in not settling for any old guy, just because you don't want to be on your own, You are only 32- lots of time!
There are things in your life that you don't like (eg job) that you may not be able to change RIGHT NOW, but you can think about, and plan for, a future time when you will be able to change things- looking forward is always better than looking back. Anf things do nearly always get better.
Keep a diary- I look back at times I thought life was hardly worth living, and I am amazed at how they turned around. This is going to sound really daft, but when I feel low/ at a brick wall I think of that Kate Bush song- "I just know that something good is going to happen...I don't know when. But just saying it could even make it happen"
Sorry if any of this sounds twee and patronising, but things usually do (suddenly and unexpectedly!) get better, so look forward