I always thought that So Cruel was about a relationship in which the two people in the relationship thought they loved eachother, but it's really only lust.
"Between the horses of love and lust we're trampled underfoot."
-they're having trouble determinning wheter it's love or lust
"Screams like and angel for your love
And as she makes you watch her from above
And you need her like a drug."
-the "scream for your love" and "watch her from above" reminds me of sex. That's followed by "and you need her like a drug." This is only my opinion but it seems he only feels that he needs her after/during sex. A realtionship of lust.
"I'm only hanging on to watch you go down, my love"."
-reminds me of oral. Maybe I'm just a pervert or something but he's only in this to watch her "go down."
So that's my opinion of the song. I could be totally off but that's my interpretation. Whatever it's about, it's a beautiful song and I love it.