I can really relate to a lot of your situation -- my husband is a lot like you. He has had so many of the same feelings. One thing we are working on is the co-dependant nature of our relationship, and how unhealthy it had become. My husband has also narrowed his life down over the years. He counted on me, so much, to be the social director and the one growing and learning, while he just went to work and came home. We realize now that he needs to work on HIM. I'm starting to wonder if my relationship with another man came from a fear of being swallowed up by my husband's neediness. He is now working on his own life and becoming more of a fully-alive human being. We are still living in the same house and actually sharing a bed, but we are "separated" in the sense that we are both free (and encouraged!) to develop outside relationships. I believe it is the non-sexual, platonic relationships that will develop for both of us that will make the biggest difference.
Ironically enough, my boyfriend has really taken a lower priority for me now that I am free to do as I please. I am really guarding myself from jumping into yet another co-dependant relationship. It is very empowering! He has become more of a teacher, for me, than just a wild romantic infatuation. Our friendship has deepened and I realize it is not just about sexual attraction; it is also about the things in him that I admire that I want to develop in myself. Wow -- who knew
While I hate the old cliche, "mid-life crisis," my husband does feel that women go through a big shift in their 40's -- I know I am particularly working on my issues of independence and balance. I had children young (I have 6) and I feel like I've never had time just for ME. So he is very understanding. It sounds like you are also a very understanding, caring man who loves his wife very much. Do her a favor and give her the BEST gift you could ever, ever give her -- the BEST you, the REAL you. Find him again! It's a great place to put your efforts, after working on a troubled marriage and all the stress that comes along with that. She may see you growing and changing, and become curious and admiring -- BUT, that is only a by-product.
Good luck, I'm routing for you guys!!!