I honestly dont know what to do anymore

i am failing my exams and feel like i failed in life. I know i can get my dad's gun but every time i think about killing myself i think about my little brother and mom. I dont think my mom actually cares tho i think she just wants to do what a mom does but my little brother doesnt even know how life works yet and i dont want him to grow up not remembering me but knowing his brother killed himself. I am honestly one of the dumbest in my class aswell so its just so embarrasing but if i do fail 9th grade i will look for the gun locker key. i dont need any replies to this i just honestly needed to express myself.