In the early '80s, I read a story about a Terran man on another planet, where the natives develop skin lesions and eventually die, but are happy, as they become part of the planet they live on. I remember that the protagonist is not developing the lesions, because he hates the planet. Once he starts loving the planet, he starts having the lesions as well. In this story, the planet is "alive".
I think you may be slightly mis-remembering "A Song for Lya" by the obscure science fiction author George R R Martin.
The mis-remembering comes in with the "skin lesions" which, in the story, are blobs of fungus/jelly that grow and slowly consume the person (who, in the end, gets joined with the group-mind/communal blob creature). Also, it's not the whole planet that's alive/linked, just the gigantic blob creature and all the natives and humans with the parasites on them.