For your wife to tell you that she lost sexual interest in you 3 years ago, but was willing to marry you 6 months ago, strikes me as saying something not very nice about her character. She's making it sound like she is doing you a favor by being with you. You sound like you are very concerned with her happiness. Maybe too much so. I would suggest you hanging back quite a bit. Show less interest. Play hard to get. She may need to be challenged. If she sees that getting your attention is something she has to struggle for a little (at least,) she may value you more. It's just a hunch I have, but I don't think you have much to lose by testing it out.

My guess is the more you jump through hoops trying to win her favor, the more unimpressed she is going to act. I don't know why so many women do this to men, but it seems to be a not very rare syndrome. And the men always seem to be such nice guys. For reasons that no one has quite figured out, women tend to be more sexually excited by guys who are not too overly nice. It's not politically correct to say this, but I do think women feel more secure with a man who dominates them at least a bit. I also believe that appearance is not the main factor in making a person of either gender come across as sexy. My impression is that deep down inside, men love to be mothered. Women, on the other hand, love to be confidently "led." As Nietzsche said, "When you go to woman, take a whip."