I want to tell my wife that I find my ex more attractive than her
How is your wife going to feel when you tell her that?
My wife will feel bad since my ex is now single.
It's wrong to compare your wife to your ex. It would hurt her feelings. You should divorce your wife if you feel you aren't attracted to her anymore.
I can never do that to my wife. It's bad enough that me and my ex hooked up again.
That is even more of a reason to cut things off with your wife. Regardless though, you should not talk to your wife in such a way. I know that it would hurt you if she told you the same about her ex.