You're very welcome. I truly do understand how you are feeling as I went through the same thing when my husband & the friend of ours were dating each other and I wasn't involved. I found myself, just like you, comparing everything he did for her & measuring it with what he did for me. It will truly drive you insane & cause more problems then it's worth.
It is very difficult to deal with, sharing that person you love most in the world. That's why trying a triad might be better suited for you as then you will be involved also & won't feel like you're on the outside or being left out.....plus on the upside you'll get twice as much attention!!!! Or maybe even try dating someone yourself.
But you can't compare & measure what he does for her to what he does for you, it will just drive you more crazy.....you have to maybe look at it from the view that it's like a new relationship, you know when you first meet someone & you get all giddy to see them, can't wait to talk to them, etc....well that's sort of what your husband & her are going through. It's new & exciting.
I of course don't know you or your husband or the whole situation but from what you've said & this is just my opinion I would say that yes the relationship between your husband & friend has progressed beyond just friends w/ benefits....they might not even be aware of it. But I definitely think there are feelings involved & developing and that's only natural.