Please help! Pregnant and trapped!?

I am seven months pregnant and living with the father. We have been dating and living to together for about 3 years. Things haven't always been easy but since we learned we were expecting they started getting better. He stopped drinking as much, gave me much affection, and took care of my emotional needs. As I get further along in my pregnancy things have gotten worse. He has been drinking more often and heavily. I suspect he is using some kind of drug. I have found remnants of coke in his nose more than once. Sometimes it seems like he is on something else. He can get really mean or mad at me for no reason. He tells me he will be a minute when he leaves and disappears for an hour to three hours. This is something I know all to well because it is what my mother did when she was using drugs. Financial burden has been placed on me and I am a full time college student, part time worker, and 7 months pregnant. I have talked to him about it and every time it seems like it turns around on me. I am always the mean one being a ***** making him feel bad. I don't know where he goes or what he does when he disappears and it kills me on the inside. If i knew it was an addiction or another female at least i could start to move on and figure out what to do. I feel like i am being taken advantage of financially. When he is broke he is the nicest sweetest most considerate person but once he gets paid again he does something else to hurt me. The past 3 weeks were good and i thought he finally understood but last night we went to an indoor arena football game. we got home at 1030 and said he was going to run to his friends for a minute. He was gone for a couple hours and then the car pulled up but he never came in. I presumed he was drinking at the neighbors house but he never answered the phone and i do not know which house his friend lives in. I have suffered from depression my whole life. My father had a drug habit and repeatedly abandoned me. Later in my teenage years my mother had an addition and stole and lied to me. I have struggled to convince myself that i am more important these substances but the man that i love has caused me to relive these feelings. I have convinced myself i need to be there for the baby when she is born but i cant even do that anymore. i am not a murderer so i will do no harm to myself while im pregnant but i have no will to live after that. Last night when he finally came home i told him how i felt. how it was getting harder and harder for me to put off the inevitable and he told me to do what i must and then left again. He came home a few hours later, slept, woke up and left without a word. i still i have not heard from him. i have no idea what is going on. i have no family. all of my friends have left my life and im so alone. the only thing i can think to do it start by moving out. Both of our names are on the lease but its my SSN. If i leave he will surely not pay and destroy my credit. if i stay i cant evict him. i really cant afford to pay one apt rent i surely cant do two. i dont know what to do. i cant take any more pain. i am so sick of feeling unlovable and worthless. please any help? advice?