Her feelings are hurt I'm sure. You essentially have 2 kinds of people in this situation. Those that are comforted by the fact that we average Joes will never get a shot at Jessica Alba and thus it doesn't bother her to catch us wanking it to her. Then there is the other type, the ones that believe in true love, and that like to think they are their lovers fantasy, and that their partner is monogamous with them, even mentally/emotionally/spiritually/whatever I think you see where I"m going. :-)
My wife and I are a type 2, she doesn't masturbate unless it's mutual with me (and I generally don't either) and we both like to believe that we don't fantasize about other people. And I typically don't so I like to think she is the same way. (even after a decade of marriage my wife is more than enough turn on for me, I fantasize about her frequently during the day and when we make time to have sex it's always a "big event" or special moment.)
Despite what you and your partner have "admitted" too, I'm sure your OH probably liked living under the notion or fantasy that if you do masturbate you do it with her in mind and now she's a little jealous/heart broken.
Do tell us how this has turned out for you.