Ok i need help with my gf im really confused?

ok so my gf and i have the attitude idc about myself but i care about u more then anything. i found out she has been smokin pot and drinkin when its available. i told her im gonna start if she doesnt stop. im supposed to be gettin some pot wed. should i smoke it and not tell her and see if she can figure it out or should i just trust her and hope she doesnt do it anymore. i really dont know what to do and i reallllly care about her like a hole lot!