Answer:
It is only a phase because both characters are very young and they attract very quickly, without knowing each other well and more because of their physical appearance. If it had been an identity crush, they wouldn't have committed s uicide because the admiration would have ended quickly, or at least it would be on a more positive than a tragic path. They could have reasoned that it was not necessary to die for each other, that they were still forming their character and maturity, with the support of their parents.