What does a guy mean when he says he feels like he belongs to a girl?

My female friend IMed me yesterday telling me that my ex talked to her the night before. She said that he asked her how to make things better between us, and he said something to her that neither her, nor I, understand what he meant.

He said that he felt like he belonged to me.

What does it mean when a guy says that?

My friend and I both didn't know, we just concluded that it sounds nice. Nothing negative.

Then he came over one night and while we were cuddling I told him that my friend told me those things. He seemed really embarrassed. So I didn't push for an answer. :P
What does a guy mean when he says he feels like he belongs to a girl?
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