I don't understand my breakup?

I'll try and keep it short. Me and my ex dated for nearly a year, he treated me good in the start but after a few months I felt he was losing interest. Everything felt forced and like a chore. He also wanted sex and I wasn't ready, which he said was okay by him. Towards the end even getting a phone call felt rare and obligated rather than out of wanting. He got mad at me for hanging out with a friend and not telling him about it. He insisted I needed to check in with him and I said no and to stop talking to me like that. He then said we needed to go on a break and broke up with me a few days later and wanted to immediately never talk to me again. He had always acted like I was so special to him, that we'd get married, and that if we ever broke up we'd stay friends. He also insisted he was breaking up with me to fix his own life and that it had nothing to do with me or his feelings for me. We never even talked about our breakup, he just dropped me. Why would it happen like this?
I don't understand my breakup?
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