I think my girlfriend is a druggie.
Why do you think that?
I think she's a bad influence on me.
It is bad to do drugs.  If she is doing them and influencing you, it is time to move on.
I don't think I can leave her though.
I understand your attachment to your girlfriend but drugs can ruin both your lives. If you can't get her to stop abusing drugs you will have to end the relationship for the sake of your own future.