Time travel, spike goes back to house in S6...

And carries on being a friend instead of sleeping with buffy.

Not sure if it's when he gets soul or at the end of angel.

Thanks

Hero's Reward by pfeifferpack (found at Elysian Fields)

Summary:Setting: Begins post AtS "Not Fade Away" and rapidly goes to S6. Given a chance to do things differently a hero finds that putting another first and ignoring his own desires can lead to his rewards beyond his hopes.

Not sure if it's the right one but Spike does travel back to s6 just as he and Buffy are fighting in the abandoned house.

It is. Thanks!