how much weed is to much weed?

im 15 years old and my brother and his girlfriend are 20ish and they smoke a lot of weed all the time. and once i went into their room and they had a disposable cart in there. i hit and it literally fell inlove (i’ve smoked weed before but this jusy felt different) and since then i’ve been going into their room (when they are home which is not all of the time just like half of the weekish) and i hit it every night and they don’t know. i love it but i’m genuinely scared like i’m gonna get into bad drugs? does that make sense? do i stop? i feel like also i’m just a teenager so i don’t know if i’m just having fun or if i’m gonna be like a heroine addicted when i’m older which i’m scared for.