Hi. I am a professional psychologist. Although my specialty is not compulsive lying, I can give you some basic advice. First, you should be very proud to have a wife that is so loyal and sweet. And you should be proud of yourself for reaching out to others and trying to get help.
I do believe that you have a strong marriage now but your problem (like any compulsion, such as alcoholism) is hurting your marriage. You are not alone. There are many others like you out there. Since you wrote this question I feel that you genuinely want help. You should try and find a psychologist near you. Many psychologists take insurance, so that might help. Call your local hospital and they may be able to recommend someone, or ask your regular general practitioner (regular doctor). I strongly strongly suggest a "behaviorist". This is a kind of psychologist that not only examines why you are lying but also teaches you new techinques to help you stop lying in the future.
I would guess that your lying (as most people) comes from anxiety and fear about normal life situations. That's totally ok. Everyone worries. You just deal with it in a different way. You need to talk to someone who can help you learn to cope with stress in a way that does not involve lying.
It will all be ok. It is WONDERFUL that you are reaching out and talking to people about this!!! Congrats!! Now you just have to follow through with the treatment. Im sure that things will work out, all relationships take work.
Good luck and take care!
PS you can also check out some online message boards for others just like you!! http://www.psychforums.com/viewforum.php?f=123&sid=00e3eea17da1a280632da81337431654