^This is the best advice. Since your wife won't budge giving you sex, and you won't seek it outside the marriage, then the only way to get her to answer for her sex-gate is to invite a marriage counselor into your lives. Someone who will know your wife's clever verbal tricks and be able to talk through those, to force her to be honest with you. If that's not an option, then, I'd suggest Divorce, as the last alternative, as others have suggested.

I know you're 65 and have children and grandchildren. Clearly, sex is important to you but not your wife. So, the only way to solve this dilemma, is to get an expert involved who will help you two reach a compromise.