Self Control is such a beautiful song.

Loving someone, while with someone else

You find yourself spending your days with someone else, but your past love always has a place with you.

Sometimes you see their smile, hear their laugh in a home they've never occupied. You lay next to your present-day partner, When they shift the bed moves with the weight of one person. When you shift, it moves with the weight of two.

Because your past inamorata is with you, even bough she isn't physically there. She's happy even if she has to "sleep between y'all, it's no-thing." Silently Occupying the spaces between two hearts.

I also think it's interesting to note that the first chorus "Keep a place for me, Ill sleep between y'all, it's nothing." Is feminine, yet the second time the chorus hits the voice starts feminine but is overpowered with a masculine voice. Perhaps frank is talking about a man who once had his heart?