You should talk to your girlfriend about it. Never lie to her.

I personally have the same issue. It’s led me down a path of sexual deviance and loneliness. Like any addiction it isn’t anything to be taken lightly. Get a hobby, and otherwise find meaning and pleasure in other things. Like spending time with family and your girlfriend. It’s not healthy to be addicted to anything, masturbating everyday can be a healthy thing. But when it becomes something you NEED to do every day and is something you can’t get your mind off of, it’s probably a problem and should work to fix it.

so what? i masturbate too, sometimes after sex too, i will masturbate if i want more. my husband don’t mind, i don’t mind him doing it too. heck he even help me with my masturbation.
it’s nothing bad. trust me.