The Other Now by Murray Leinster

 It was self-evident nonsense. If Jimmy Patterson had told anybody but Haynes, calm men in white jackets would have taken him away for psychiatric treatment which undoubtedly would have been effective. He'd have been restored to sanity and common sense, and he'd probably have died of it. So to anyone who liked Jimmy and Jane, it is good that things worked out as they did. The facts are patently impossible, but they are satisfying.

Haynes, though, would like very much to know exactly why it happened in the case of Jimmy and Jane and nobody else. There must have been some specific reason, but there's absolutely no clue to it.

It began about three months after Jane was killed in that freak accident. Jimmy had taken her death hard. This night seemed no different from any other. He came home just as usual and his throat tightened a little, just as usual, as he went up to the door. It was still intolerable to know that Jane wouldn't be waiting for him.

The hurt in his throat was a familiar sensation which he was doggedly hoping would go away. But it was extra strong tonight and he wondered rather desperately if he'd sleep, or, if he did, whether he would dream. Sometimes he had dreams of Jane and was happy until he woke up, and then he wanted to cut his throat. But he wasn't at that point tonight. Not yet.

As he explained it to Haynes later, he simply put his key in the door and opened it and started to walk in. But he kicked the door instead, so he absently put his key in the door and opened it and started to walk in—

Yes, that is what happened. He was half-way through before he realized. He stared blankly. The door looked perfectly normal. He closed it behind him, feeling queer. He tried to reason out what had happened.