Blake’s ‘Clod and the Pebble’: is love unselfish (the Clod) or selfish (the Pebble)?

Love seeketh not Itself to please,
Nor for itself hath any care;
But for another gives its ease,
And builds a Heaven in Hells despair.

So sang a little Clod of Clay
Trodden with the cattles feet;
But a Pebble of the brook,
Warbled out these metres meet.

Love seeketh only Self to please,
To bind another to Its delight:
Joys in another’s loss of ease,
And builds a Hell in Heaven’s despite.

You can compare different versions of the poems here.