Can i get some advice on this situation?

Im 20 years old. I was going out with my boyfriend for over a year. During this year we have had many problems. One of them was trust. I didnt trust him because he went behind my back and did stuff he shouldnt of. He doesnt trust me for something i did before we started going out. All that stuff right there should of told me we had a horrible relationship, but theres more to the story, and im still confused. A few months ago we were fighting and he shook me to calm me down. I told him to never do that again. Like a month later, he threw a shoe at me cause he was mad, and a few weeks later, we were fighting in his truck, and he reached over my side and opened the car door and started pushing me out. I broke up with him that day. I met a boy who is older nicer, and he is so sweet. I have been hanging out with him and he likes me alot and says hes going to treat me right. I still talk to my ex cause im starting to miss him. We loved each other a lot, but i didnt like the way he was treating me. He understands that, and wanted me to give him a another chance to change, even tho everytime he did something, he said hed work on it, but now he says he would do whatever it takes because he wants to change for himself, not just for me. Am i just scared cause im so used to him and comfortable with him that i dont wan tto be with anyone else? I think i just really do miss him. I dont really no what i think actually. I thought breaking up with him was the right thing to do, now im not sure.