Someone please help me, should i walk away or try and work things out?

In November 2009 i met my current boyfriend Tom, We clicked straight away and always done stuff with together as we had the same group of friends. Tom told me he liked me but i had just got out of a relationship therefore was not ready for another one. As the months went on we became best friends and spent many nights in together with our other two friends, we constantly text and called each other and it was clear we loved each other but i wouldnt allow myself to trust him. I spoke to Tom about many things and he would do anything for me, he made me feel confident again and always made me happy. In April 2010 we finally got together and it was amazing, not much changed and we saw each other everyday as we would when we were friends. I stayed round his and all we would cuddle up together and watch movies, its was so different from any other relationship i had cause he treated me so good. Unfortunately around November time we began to argue alot, and i found out he had lied to me and was doing weed behind my back which i am against due to family issues. Tom knew this when we got together and he knew why so i couldnt understand why he didnt respect that as he was such a nice person. He began calling me name, pushing me around, and then crying and saying he was sorry. I was very confused at this time and developed depression and anxiety. I would suffer from panic attach, lack of sleep, low confidence, i was at my lowest i had ever been in my life. When i found out Tom was doing weed i finished it cause like i said i dont agree with it. Tom has a bad upbringing, his mum is a alcoholic who has been violent infront of him and towards him, and his younger sister died. He told me he would stop doing it and he did stop so i took him back, i blamed his behaviour on the weed. But unfortunately the behaviour didnt stop, he started saying stuff like your ugly, stupid, i dont need you, its over, that i controlled him and he could do better. I used to cry my eyes out cause i didnt understand why he was doing it, i felt so low but then when i would threaten to leave he would say he was sorry start crying and be really nice to me for a few days, calling me beautiful, and that im the best thing that ever happened to him. Sometimes i would retaliate to some of the nasty things he said to me which i know was wrong but any normal person would. Tom didnt have a job over this period of time and i would pay for his fags, nights out and anything i could pay for. Eventually after a few months of dealing with his emotions i finished it. I ignored his calls, texts and messages. After a few days we met up and i acted very confident, he tried everything to get me back and he was truly the Tom i fell inlove with, my best friend. We took things slow, and i constantly reminded him i would leave if he done it again, eventually we built our relationship back up. Tom got offered a job and everything was looking up, although the job didnt work out. We were planning on moving in together and i was so happy. But over the last few months his started going back to how he was, telling me its over, walking out on me, telling me he dont love me, i tried to ignore the behaviour as it didnt make me hysterical like it did before. I am now in �420 debt as i have had to support both of us became my new start date was delayed and Tom has not found a job. Last night he told me its over cause i left my bank card at my aunties so i couldnt give him ten pound from his job seekers. He walked out my house after calling me ugly, stupid and that he didnt love me. I went for a walk and the texts started.. I love you, im sorry, can we talk? I love Tom so much i really do but i just cant go on like this, i want him to be the person i fell inlove with and i just dont know what is wrong with him. He keeps calling, texting, but i dont want to speak to him. Why is he being like this? Has he got a split personality? I dont know what to do and im all over the place. I would stand by him through anything but some things you just cant take. How can i help him? Or should i just walk away even if it breaks my heart to.