Your right about one thing. The issue you have is a foot fetish. Most people with a foot fetish includes it in there sexual acts, or even helps them to come to that point of total satisfaction. Then there are others who have a foot obsession to were they can lay under someone's feet for hours without taking there cloths off at all. Almost like being in a different world by feeling secure, or having a calm affect from the scent the feet gives out. No one really knows why it calms our hormones, or gets the hormones very active. I know in my case, I divide to two. I am able to have a sexual relationship without touching the person's feet at all. Then on the other hand, I love the scent of feet when I go to sleep and not involve and sexual act. Yet, I have no interest in feet when I know there clean, or when someone walks around bare footed or in open toe shoes. There are many different aspects in people with this type of problem. All I know is, it has a great control over me that I can't help or need. I had this even at the age of 5, and now I reach 60. Nothing has changed, and I never grew out of it.
No one really knows why. In most cases, it starts very young - as early as 2 from some of the posts on this website. You are blessed to have have such an accepting wife! I say just enjoy it and don't question it so much.
Foot fetishes are very very common! There's stuff about it all over the internet and some have said it comes from when we are children we look at peoples feet alot, especially our mothers. I used to know someone with a foot fetish, it was cool!
Have fun!