My first boyfriend is/was a narcissist and he broke up with me. Help

I am 21 and in my senior year of college. I always withheld myself from dating anybody because I never truly found anyone that I could see myself with, and didn't feel I was ready.
About a year ago my ex-came into my life unexpectedly and pretty much forced himself into a relationship with me. I constantly would tell my friends that I didn't want to be with him and didn't like him but his persistence and constant praise finally wore off on me and I gave in. The beginning of our relationship was great, because of the way he treated me I constantly told my friends how confident I was in him never cheating on me. Whenever I pulled back he would reassure me how much I meant to him and how he loved me, basically telling me all the right things that I wanted to hear.
My only problem with our relationship so far was that we would never let me even glance over at his phone, and if I did he would pull away and lock it and put it away. I always thought it was suspicious but decided to look past it.
About six months into our relationship I had a dream that he was cheating on me and for the next couple of weeks after the dream, i had a strong burning feeling it was true. I told him about the dream and we laughed it off, he didn't feel phased. A few weeks later he came home very drunk from the bars, and I decided I just needed to look through his phone to ease these crazy thoughts that were going through my head about him cheating. Low and behold he had texts from another girl talking about him sleeping over that following night and them getting breakfast together.
Come to find out, he has been dating this other girl longer than I have been with him, he's even met her family and went to their family Thanksgiving... and then drove to my family's Thanksgiving right after.
I was so in shock and taken back, and he was so drunk he had no idea what was happening. I grabbed my stuff and went home. He texted me the next morning asking why I didn't go over his house last night and I explained to him that I knew everything and the worst part is he just admitted to it and never said he was sorry. Telling me "cheating is just something that happens".
For some reason, I just tried to get over it and stay with him. Hoping he would never do it again and everything would go back to how it was before. Everything got very bad and quick. He would manipulate me into buying him stuff, paying for his car payments etc. (I soon learned that he has done this to all of his other girlfriends too). If I didn't go get something from his car for him or make him breakfast or go buy him food he would give me the silent treatment for hours. He went through my phone and saw that I was talking to someone that I used to hook up in just a friendly manner and told him multiple times that I had a boyfriend and I wasn't interested in him anymore, and that I could never cheat on my boyfriend. He freaked out on me and broke up with me, then after me begging for his forgiveness and he would take me back and everything would be fine.
He did this to me probably 5 times in the span of the last 2 weeks. Telling me I'm psychotic for asking who he is with or who he is texting and freaking out and just leaving everytime something would happen.
I would ask him if he wanted to be in a relationship and if he loved me and he assured he did but when I asked him why he couldn't say the three words he told me he didn't tell anybody he loved them, I should just know it... even though he told me all the time at the beginning of our relationship.
Today he broke up with me again, because I asked him who he was texting. He told me he was never going back and he hopes that me being psychotic was worth it and that maybe I can find someone else to obsess over.
These are only some of the things that happened there were many other girls, ex's involved I could go on and on. My question is where do I go from here? Am I crazy for looking through his phone and asking him who he is talking to? This was my first relationship and I had no idea what I was doing and now I'm so stuck, I feel like a year has flown by and I'm so stuck. I can't help but believe i am the cause of us breaking up and I dont know what to do to move on. Him and i were together whenever we werent working or in class and slept at eachothers house every single night for almost 6 months straight.