He won't return my stuff after he broke up with me, why?

He stormed out of my home (he was hurt because my adult children are not fond of him) and then wrote me horrible Facebook messages saying he was done and will not return calls or emails asking for my things back. He has my house key, dishes, and clothes of mine at his place. I have his house key, clothes and things at mine. We dated and we engaged for 5 years.
He won't return my stuff after he broke up with me, why?
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