Gwyn-- What you are describing is an addiction. I have BEEN there, in all seriousness. I get how you feel sick without him. I actually contemplated suicide when I went through all my mess. I committed myself into the hospital, twice.
It is hard. You might very well need help to break free of it. You have said yourself that you know, intellectually, that this is toxic. I know how feelings can be overwhelming. Do not rule out meds - I needed them for the anxiety and depression.
Try to get to a 12-step group. Co-dependents anonymous is the best fit, but they all deal with the same issues. If there are no meetings close to you, go online. Read the literature.
Hearts are stupid, simple things. They react to not only what is happening now, but also all of your old, un-dealt-with issues and what is comfortable, even if it is not healthy. It is time to lead your life from your head.
Good luck....you deserve so much more for yourself.
