you give us no info here, we can't tell you if it's safe or not. If you are new to coke then start very slow and with small lines. Coke can be pretty cut and shitty if your stuff isn't quality which might have you feeling like shit if you do to much.
If your girlfriend doesn't know you do coke then you should probably not take any since you said you are new to it and have a higher chance of blowing it.