Something I realized about when James got the letter
In the first few moments of the opening cutscene, James probably has not yet made up the lie that Mary died of illness 3 years earlier and beckoned him back to their special place in a letter. At least this is how it seems in the remake. His hands are shaking, he is sweating, he is staring at himself in the mirror. But then he kind of pauses and calms right down. His demeanor is totally different, almost dissociated, and then we see him leave and we get the cutscene about him getting the letter.
I think that he was originally in that bathroom to psyche himself up for what he intended to do. He came to Silent Hill with Mary's body in the car in order to kill himself by driving into the lake. At the last moment, he almost chickened out, and got out of the car to try and gather his courage. He didn't even close the door to his car, so he was probably planning on getting right back in and driving it off a cliff. It was then, just as he looked at his reflection in the mirror, that Silent Hill's mysterious power obscured the truth from him so that he might have a chance to work out his inner demons and find peace.