"Me so horny" - that's got nothing to do with it, it just made me laugh.
Hehehe seriously, I don't think I can do any better than what's already been said, but we say "long time, no see". "So long" is how Americans sometimes say goodbye. I assume it must be referring to a journey that will take a while, or possibly "a long time" before they see each other again, meaning they're very fond of each other, and any time apart will feel like a long time. So heavy, so funny, so long etc
We never say "so long" unless we're copying Americans for some light hearted banter, like we may say "howdy" like a cowboy. The only times I like wonky English, are when it's funny or when it fits music.
"so long, no see" pah!!
But nothing wrong with Stevie Wonder's, "It's been so long, since I've felt a wanting hand, that I feel the world's cold, been so long, that I say to myself, it's time to find myself again".
Oooh the irony :) "now put her in the buck!" :D