I agree with cypher. Hell I still masturbate when I can't sleep at night. I would say though that if you are more interested in masturbating than sex with your g/f then you are not getting a need met by your g/f that is being met by masturbating. It could mean that you are gay if you had gay thoughts when you masturbate. Or it could mean that you asexual which simply means you are uninterested in sex with another person. Or it could simply be that your g/f just doesn't do it for you.

Regardless, no of these things are bad for you, it just means you will have to take a non-traditional approach to your sexuality.