?

well both of them agreed that they would grow up and become responsible first and the uke himself said that we would wait till the seme becomes a fairy

Hmm I think it's more like that no matter what he still have to go, and lookin' for another people who need his healing power to increase his own level too so when he become the high level fairy he can stay whenever he want with his love

It's called "unselfish" love because they understand each other's circumstances and not lock up the other one coz they don't want to be left behind.

Love, I don't know if you are seriously asking... But here it goes... It's called responsible, unselfish, trusting and unconditional love... Neither of them were in the place to love freely and or to the fullest, yes, they were right for each other, but each of the parties involved had to continue with their own lives in order to achieve their dreams, they trusted each other, and loved each other enough to know that time and distance wouldn't change their feelings. If you still don't understand it, I really hope you get to experience it, it's amazing to know someone out there loves you enough to respect you and your dreams, and will give you freedom and time to achieve such dreams. If they had continue with the relationship, then, probably, resentment would've grown, and with it, distance, sometimes, the best way to show love is via respect and trust.