Star feels constant guilt because she's supposed to be with Tom but yearns for Marco



Marco feels constant guilt because he's supposed to be with Kelly but yearns for Star, and possibly interferes with Star's potential lifelong relationship with Tom



Tom feels constant guilt for being a bad boyfriend in the first place, playing the part of an immature and obsessive ex, stealing his best friend's significant other, and cursing both his best friend and his girlfriend to a fate of endless unfulfilled desire against their mutual wills



everyone is trying to do the right thing, and it is killing them all inside and it HURTS to watch xP