You are being treated as bait. You are the bait for a fish. The important part of this is "You are hooked". The rest of the sentence is ONLY there to be funny. You are hooked means you like something (like a possible life partner) and you do not want to be let go. by the way Hooked = Addiction So this is a pun between a fish hook and addiction of love

Without context I have no idea. Cast aline = comes from fishing, where you cast the line into the water to hook the fish.

The world cast means "throw out", like "throw out a fishing line or fishing net. "Cast a stone" would be throw a stone.