Why am i depressed or sad so much?

i'm 18 years old, male, and i just get really depressed about stuff alot, and sometime just find myself crying while laying in my bed at night, or getting unnecessarily drunk to help me deal with the pain, whenever i think about my mom bailing on us, or even when she was around, just a bad environment, with her screaming at me and my little sister back in the day, and when i was a really little kid i was really scared of my dad, he used to beat me on a whim, i would have nightmares about him (had to go through 2 pretty bad divorces once as a lil kid, and once when i was like 12) , or cant find a girl who's right for me(i think some of my girl troubles have alot to do with the relationship with my mom, but i dont know), and me and my dad ain't that close, i mean we are cool, but i can't really talk to him about this sh1t, and now my mom is addicted to drugs somewhere, i keep to myself about my problems for the most part, sorry if this is unorganized, i have a hard time putting it down