Well, as I'm sure you know, anal for men can be an extremely pleasurable activity. This is chiefly due to the fact that the prostate is being stimulated. Being gay does not mean that a man likes anal, it means he wants a relationship with another man. I actually have a gay friend who loves his boyfriend but does not care to have his butt played with... but he loves his guy, and finds men attractive.
You need to explain this to your wife. Tell her that you love her, and find women attractive, not men. Tell her that this is simply a physiological thing, that the prostate gland is being stimulated and that is what feels good... the shape of the toy simply happened to stimulate you in a way which felt best for you. (some women like long dildos, some like curved, some like straight, some like short and fat.. etc etc... it's not any different for men..)
I hope this helps
