I would say see a doctor but I'm sure if you have been dealing with this for 14 years then you have been there done that. I'm also going to consider you have done counseling and/or medication. I'm not a doctor and may not have a clue what I'm talking about but you already admit that there is nothing really wrong and all of the bad things are in your head only. So with that in mind I would say pick the farthest point that you can go away from your home and ride/walk to that limit every day for a week (or how ever long you think is best, but once you decide on a time frame stick to it). After a week when you get to that limit choose a point; the next block, road sign, tree, what ever and go to that point for the next week, then move to a farther point. Have your girlfriend go with you if that would help for support.

I might be way off; I don't know I'm not a doctor, but if you where looking for a doctor you probably wouldn't be posting this on a cycling forum.

Good luck with your fight and don't give up.