I've heard this song countless times and I never really thought about the meaning of the lyrics. So this song, like many other Bruno Mars songs, is describing a romantic/sexual relationship. He's saying that being with this woman is like being in heaven. Like he didn't know what he was missing until he met her. Like he was "locked out of heaven" because nothing else has ever made him feel this way.

Is this from a popular love song or poem? I'm guessing that the speaker (I'll assume a man) is in love with someone and they've gotten into an argument, or he's done something he regrets, and his love is angry with him and is not speaking to him or has broken up with him.