Blindsided with a break up?

I was just blindsided by a breakup last week and am struggling to wrap my head around it. Everything was perfect, we never argued, had similar interests, got along so well with his family and friends. He treated me amazing and constantly told me how much he loved me.

One night last week he went on about how it was our anniversary, how lucky he was, and how much he loved me. 3 days later he told me he decided to break up with me.

What causes this? Any insight here?
Blindsided with a break up?
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