Why do guys keep your stuff after a break up?

I asked for my house key back after the break up, to date he has never given it back.

Why would he not return the key?

Trying to understand this behavior from my ex..and he ended the relationship during a row.

So yes I know he was angry, but I waited to ask for the house key back 10 days after the break up hoping he had calmed down.

Why do guys keep your stuff after a break up?
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