If Rosario's character was "The Light" and in fact princess of Zartha, why can't she visit Will's character? Or, if she absolutely cannot return to Earth, why not send a ship to pick him up and take hi to Zartha? They obviously have the technology because they had that pod that took her back to Zartha.
sharewell I am just making stuff up but here goes:
if you figure a long distance relationship between two people in different states is hard to keep then how could they have a lasting relationship in different parts of the universe?
It may also be possible that their might be MIB rules that they are not supposed to have romantic relationships with aliens or at least big wigs but again I'm guessing.