Compared with other relations, the time for a pedophile relation is much more limited. The child becomes an adult, and the sexual interest of the pedophile ends. This is more problematic for boy-love, because the difference in sexual attraction between boys and adult men is much greater compared with the difference between girls and women.
This end may be harmful for the pedophile. And not only at this end, but all the time the pedophile knows that there will be an end.
I think, this knowledge is something like the general knowledge that we will die some day. We know it, but we don't think about it very often. Because to think about it is harmful. But, on the other hand, if we think about it, we give higher weight to each moment of happiness. Thus, it is not only negative. It can make the live more intense, help us not to loose the time.
It may be harmful for the child, if the pedophile drops the child and leaves it alone. But this is not the necessary end of the relation. The decreasing interest of the pedophile is often in some coincidence with the increasing interrest of the boy in girls and a related lower interest in sex with the man. The sexual relation can simply become a non-sexual life-time friendship, or it can end in harmony in a moment there above sides are no longer interested in a continuation.
There is also the question of the moral value of a relation with a predefined end. But the ideal of life-time love is far away from reality for the other forms of sexual relations too.