On snooping-The squeeze is definitely not worth the juice. The biggest problem with snooping is the human condition. That is because you will see/hear/find what you fear the most....no matter what you find. Example-She goes out to lunch with the girls. You see the debit off the account at 2....by 5 you know she had lunch with the OM. After your stressful ride home from work you are angry and out of control....over a lunch out with the girls. What you find may not always be what you think it is....more often than not it is something totally different....The Human Condition.
There are books on co-dependence....I would recommend getting one. As Bworl noted...all marriages are dependent to a point. It is hard to identify over dependence, but one worth the work.