I read a short story many years ago that I think was Ray Bradbury's, but can't remember the title. It's important I find it now, so any help would be appreciated....it is about a young Martian who, when he passes too close to people, changes into what/whom they want him to be. As I recall, he passes within the "thought range" of an older couple who lost their son, and he becomes - for them - that son. He goes home and they live happily for a while but eventually they come back to town on an errand and he walks too close to someone else and becomes that person's desired person. I think in the end he goes into "melt-down".
If anyone can tell me which story this is, I would be ecstatic! Thanks

The story you are looking for is called "The Martian." It is one of the chapters in Ray's novel, THE MARTIAN CHRONICLES.