I'm so sorry you feel this way. I hear a lot of sadness in your posting and I feel certain there is a lot going on in your mind and heart besides a vague "I did not want this life." It's easy to pine for things that never were because they seem so desirable, but what direction would your life have taken if you had not had children? Had not married the man you married? Would you be....in a different career? Would you have gone on for further education? Traveled more? Moved to another area? Sit down and think about what exactly it is that you are missing, or mourning, or have somehow lost -- what specifically you seem to have missed out on, rather than just "This isn't the life I wanted." What WAS the life you wanted? And is the life you wanted at the age you got married and had kids (teens? 20s?) really truly the life you would want back now? Or are you uncertain what it is that's missing and what you would want to replace it?
All this cries out for professional help. Please, please, before you find yourself distancing yourself from your husband, before you realize your kids are nearly grown and you didn't really get to know them well -- please see a counselor or psychiatrist tomorrow and try to find some specific help for your unnamed dissatisfaction. You can find ways to cope and get yourself back into the life you ARE living rather than waiting and wondering about a life that never was.
We can advise you all day long on Mamapedia but we are not professionals and can't diagnose you, or delve into your past before you got married and had kids, or figure out if your marriage is the issue, or probe whether there are other things going on. You do not have to live like this -- take control and get help, not just our advice. If money is an issue, see your primary care doctor and ask how to get low-cost counseling and help paying for medications if needed -- such help is available. Take care of yourself, stay physically healthy too, and pursue your mental and emotional health for your kids' sake and your own.