How can someone change so much?

We dated for around 2.5 years. We understood each other so well and everything but then he went to college started being distant and I tried to be as understanding as possible but I couldn't help but tell him how I felt.. How i felt he wasn't making any efforts at all or how he just talked to me as if it was just some duty he had to do. He never reacted positively. He said he was doing everything the way he was always.. Then he came for my birthday and we were together for a week.. After a month of that he broke up on a very silly reason... I dont know.. Its been 4 months.. And I just want to make him realize how he made me feel.
How can he change so much.. Its like he never loved me.
How can someone change so much?
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