i think the first item that needs to be addressed first before anything else is why your wife is the way she is. there are many reasons why someone becomes uninterested in sex. many times it isn't that they are uninterested in sex, but rather uninterested in sex with you.
if she has lost respect for you in any way, or she feels you have lost masculinity, she no longer feels appreciated, she feels like she settled for you, or has the hots for someone else it could mean the marriage is doomed. many times people stay with their spouse even though they are unhappy because it is easier than starting over.
I have friends that had sexless marriages with the same story of the wife not interested in sex, and eventually divorced. within a month the wife had a new boyfriend and was putting out regularly.
My wife and I were on that path and I quickly realized she lost respect for me a few months prior. I repaired that by rebuilding her respect for me and trust with me, then things got hot and heavy again. I had to start acting like I did when we first met. taking her out on interesting dates, bringing excitement back into her life, showing what fun I am to be with, and that other women wanted me. Then slowly started being more vocal about how I want her, and being more physically affectionate (holding hands and what not). she used to turn me away, and not even hug me or say hello when coming home from work. now I have her doing everything I could want plus.
I think the priority should be your wife and marriage. side pussy should be second IMO.