It's forbidden for angels to fall in love with humans. However, when an angel does happen to do so, they lose their wings and become human themselves.

And when that angel passes away in the human realm, they cannot return to Heaven. But, they do not go to Hell either. Their soul is merely lost in the rift between life and death for eternity.

One angel in particular disagreed with this restriction on love. He believed that love should have no boundaries, human or angel. He believed that love could transcend the thin line between life and death. He believed that love was limitless.

I have come to love you now.

There's no place for me to go back to.

My wings have been taken away.

Even if I've lost eternal life, the reason why I'm happy

Is because my forever is now you, eternally love.

                                                    -Angel/Into Your World by EXO-K