How can some guys be so heartless like this? How could he move on so fast? Why did he lead me on?

So a guy I started dating asked me to be his girlfriend. He said he loved me and that it was love at first sight. He said he wanted to meet my parents and be committed, exclusive, and try long distance when I go back to school. He invited me with his friends and coworkers and introduced me as his girlfriend. He constantly reassured me that he wanted something serious. However, he started making excuses as to why he couldn't see me or call me. I often texted him asking what was wrong, if I had done anything wrong. All he said was no, I am just busy. On his days off sometimes he wouldn't be able to see me because he was "busy all day". Yet, he'd call me and tell me passionately that he loved me, that I was breathtakingly beautiful. I was constantly emotional, given I have NEVER liked a guy at first sight as much as I liked him. When he said it was love at first sight, I thought he felt the same. I found myself constantly asking him where he was and why he could t contact me. Until one day, when he stood me up and I got upset, he broke up with me, saying he couldn't handle my clinginess. I didn't talk to him for a week, and then I texted him apologizing for my clinginess and then he said he missed me and stopped texting. I called him kinda mad the next day, saying why would you lead me on? You say you love me but you clearly don't. And he said I'm nineteen I am not going to prioritize a relationship over other things and that he couldn't handle me yelling at him any more. He said we're not together anymore you shouldn't be yelling at me or caring this much. I said a week ago you said you loved me, and he's like so what it's over I'm moving on. And I was like why did you say you missed me? And he said I do miss you but I have no intentions of dating or seeing you again. He said, you're more in to this than me at this point because I already broke it off. I so felt like this guy led me on, he said he wanted a relationship and now he's saying why prioritize one?
How can some guys be so heartless like this? How could he move on so fast? Why did he lead me on?
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