Why would he say he loves me then leave?

So I met this guy at school about two months ago. He sat down next to me, we flirted, exchanged numbers, then we started hanging out a lot. He asked me to be official so we started dating. It didn't last very long though. We broke up, because I had a ton of trust issues and found myself doubting him. He found another girl the next week, but then broke up with her. Give or take a month, we decided to give it another try. I felt like things were a lot better. We were trusting each other a lot more, talking more, opening up more, and spending a lot of time together. He even told me that he loved me.

We had sex for the first time, and it was amazing. But the condom broke, and I started freaking out telling him I didn't know if I could see myself being a parent. I was freaking out and yelling at him. He said he wanted to be with me for a really long time, and could see himself fathering a child with me and even marrying me one day. After that day, he went to work but he kept texting me and just saying how much he missed me and loved me and wished I was with him. The next day he was texting me all day while I worked. He kept asking me to come over to his place at night, but I told him I couldn't because I was tired and everything. So we talked on the phone.

The next day we hung out, and things were really weird. He was really quiet, not saying much, ignoring me, seemed really irritated. I kept asking him questions, asking him why he wasn't talking to me, and accusing him of just using me for sex. We kept talking about me possibly being pregnant and he said well he'd be with me no matter what but kept ignoring me. So I asked him to come in and get the morning after pill with me. We just kept arguing, and he was not being very nice to me about the whole thing (even though he paid for it). We then went to the park and the whole time, he was quiet, wouldn't talk to me, and when I accused him about using me, compared him to my exes, and that he didn't care he just got mad and then pushed me away.

That night, he told me he was going to party and smoke weed and do drugs (which he told me he doesn't do) then broke up with me over a text saying he "just wasn't feeling it anymore." I just cussed him out and everything and said you were exactly like I thought you were. And all this stuff about if I'm pregnant that I'm suing him and taking him to court. And then I asked him why he was breaking up with me. He just said that "he really likes me but doesn't know what he wants. He's tired of me accusing him of being like all my exes and not trusting him. And also that it seemed like I was gonna break up with him so he broke up with me first."

I just don't get how someone can say they're so in love with a person, and would be there for the possible baby, and then just leave?

He hasn't called me or talked to me or anything in a week. I miss him so much, and even though we had our problems, I still love him a lot.

What's your problem anyway? Picking a fight with a random person? And you can't even show who you really are? I already think I know what your username really is...