Dear K,
You said that your wife’s teeth are not normal, means what? She is wearing dentures? It’s not clear to me. You feel that you are being cheated but I think 10 years is pretty long time to over come that feeling. Secondly, apart from feeling of being cheated, I guess; you must be having other emotional issues with your wife and that is why your married life is not so good. In such condition it is likely that you fall on some one. Girl of 18 falling in your love may also have strong dependency need (unconscious search for father figure). What you need to understand at this point is both of you have different need and expectations from the relationship. Both of you should be very clear on this and should discuss in depth before going to get married. You should also remember that age difference is 20 years, think of your life after 10 years. Priorities of each decade of life are different and you have distance of two decade. Do not think of short term, marriage has long way to go. To love some one is very different then to have a successful married life. Continue this relationship for at least 3 years; picture will be clear by itself. If you have sustained and compassionate relationship after 3 years, consider marriage.