I regret that the term "monoganistic" escapes me. It is not one used in the mental health profession... but I see it frequently used in place of monogamistic (meaning, being wed or mated to just one person). If you mean monogamistic, well, you *are* wed to just one person, but it sounds like you're "mating" with more than one, yes?
What your question begs, I believe, is the question... "Do I *want* to be married to this woman?" Your behavior with other woman suggests that there are problems at home in your relationship, as does your wife's behavior toward you.
The best way for you to begin to answer this question is, I believe, through individual counseling (if you're not ready to pursue this with you wife) or ideally couples counseling (if you're both looking to improve your relationship). A licensed mental health professional (LMHP) would be able to provide this kind of work with you - emphasizing communication skills as well as clarifying your needs as an individual and your wife's needs (if you pursue couples work). When interviewing a potential LMHP for work, I would ascertain if the therapist has experience working with couples - as this will be crucial to your outcome.
By the way, this does not sound like a "mental disorder," but more like an adjustment disorder. You both have adjusted poorly to some aspects of marriage and, I suspect, to your wife's recent brush with cancer and recovery. A LMHP may discover other issues during therapy, but I don't think you have to worry, at this point, about putting out a second mortgage on the house just for therapy. Find someone you like - and try 6-8 sessions... see what you learn about yourself and about your couplehood. You may find you need additional weekly sessions, or that you can reduce to monthly "check-ins," or terminate altogether. Many people find that even brief contact with an objective viewpoint can help to clarify questions which seem cloudy right now.
I hope you find this helpful. Best of luck to you.