I like the suggestions for a private investigator if in a marriage with assets things have deteriorated to a point of this being a consideration.

Is marriage counseling an option?

To add: the issue I see that could arise with you the op doing the tracking is that it could truly affect your emotional well being as it can lead to heightened obsessive/compulsions and maybe finding things you aren't going to want to view alone or getting to the brink and looking for things that may not be there. Almost akin to the spouse of an alcoholic driving themselves sick counting or looking for evidence of use etc... It's a slippery slope.