How to you know if its right to stay with someone or leave?! help me please?!?!?

ive been on and off with this guy for two years. Hes kind of a loser and i dont trust him. Yet i cant get away from him im so scared of breaking things up again, yet im even more scared to stay. He has a drinkin problem and I do too but i was better wen i wasnt with him focused more... latley ive been drinkin again with him and missin class (college student) all he does diliver pizza as a living. Im scared to be alone im scared my family hates him they dont kno im tlkin to him again ...please any advice would be great