Ill try my best to describe it.

Its about a sickly boy that is a prince (or some noble person) confined to his room/house because of his weak composure. There is a barrier past 2 trees that lead to some other land and the boy goes into the woods and finds a injured man there. He was from the barrier. He often visits the man in the forest. When the boy's grandfather finds out that he left he is very mad. He tries to see hi while its raining but caught a cold. The man takes him to the other world and there he recovers really quickly. When he gets back tot his world, he becomes sick again. THe air is bad for the other man so he cant stay long. That is also why his father is gone. In the end the boy is allowed to live with the man from the barrier.

hope thats enough, thanks.

Koi wa Maiorita, possibly? I think the second chapter had something along those lines, but I am unsure...

thanks, that the one.