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Sorry to hear of the situation. Just to clarify, is your wife doubtful of the possibility that you can improve your self esteem (and as a result improve your marriage)?
Psychologists often work with people to improve low self esteem and I would suggest you show her this self help program here - http://www.cci.health.wa.gov.au/resources/infopax.cfm?Info_ID=47 .
I use this program with clients regularly and it contains detailed information on what exactly low self-esteem is, how it develops, how it is maintained and how it can be improved/changed. The information in the early modules is quiet detailed and if you were to take her through it she would see the theory/mechanics behind how we are able to make changes to low self-esteem. You could also refer her to the literally hundreds of treatment books written on the topic, all of which clearly stated that low self-esteem can be dramatically improved.
I hope this is of some help. Let me know if you have further questions or if you would like me to clarify anything I have posted.