I can't say that you are totally wrong but Love is not a thing where terms of "someone deserve someting" cand be used. Yes these closenes were fasterned by the alien attack. But they love each other, Kurono even were going to commit suicide when she dissapeared. If we use cold logic that thats were really stupit since Reika will be just nice replacement. But Kurono does not began to meet Reika all his thougs were centered on returning Tae back. Tae is a good person for Kurono actually Kurono as a really strong person just need that kind of girlfriend, not crazy like Kishimoto or strong like Reika. Kurono and Reika can become really good friends or partners they can even become a lovers but they never can become as close as Kurono and Tae, Since Kurono and Reika are bouth strong and independed persons.