He offered me "the key to his heart"?

Been hohoking up with this guy for a year and have great chemistry. After coming in from doing a bit of groceries (ingredients to make cookies). Then he jokingly said he wants a key to my apartment. I was like haha why and he said "I'll give you the key to my eart". we left it at that. What did he mean by that?

Wh he was leaving I have him the cookies and he said it was sweet of me. I asked him if I'm seeing him next week and he said "maybe, text or call me". I asked him "you sure" and he was like yes. I almost never text him first. We talk on the phone phone sometimes to plan a day. Should I text or call?
He offered me "the key to his heart"?
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