Is it normal for a married man to masturbate to porn?

I got married not long ago. When I first started dating my eventual wife, we would have sex every time we hung out. However, the frequency of sex has been declining lately. Now we are down to once or twice a week. I'd prefer to have it every day, but she's the reason for the decrease in sex.

Another thing - she does not work, so she cannot blame being tired on that.

I'm disappointed in our sex frequency and have started masturbating when I feel backed up. She once asked me never to look at porn anymore, but I still do and I don't see anything wrong with it if she isn't giving me enough sex.