Am I normal or am I a perv?

I am a man. My wife and I have a healthy sex life, but I still m@sturb@te a few times a week, usually in bed, while my wife sleeps. but to get off, I fondle her behind. When I whack off and she isn't there, I don't have a problem. I can whack off anytime. But in bed, when she's lying beside me, I can't get off unless I'm touching her somehow, usually her behind. She knows about it as I've waken her up once or twice by being too grabby. So it's not an abuse issue. It's just that I need to feel her. Why is this? And don't suggest that I wake her up to get her involved. Like I said, we have a healthy sex life> The evenings we don't have sex, it's because she's too tired or not in the mood. So I let her sleep and take care of myself.