These aren't all human but can be pretty sad.
Fallo by Batdz Angel
Summary: Fallo. To deceive
The Wind is Piercing by Batdz Angel
Summary: Returned to the world she died to save, Buffy is unable to face those who resurrected her. When Spike is accused of keeping her from her real family, she reacts in a way no one had ever thought was possible. SPUFFY, AU AfterlifeSeason Six.
Bag of Bones by Shadowlass
Summary: Spike's return to Sunnydale, version 3,892. Nobody's rolling out the welcome mat...but someone has got a little surprise for him. S/B. COMPLETE
Five Stages of Grief by Casscaro
Summary: A series of five paired scenes based very loosely on one model of the five stages we go through when we grieve: Denial, Anger, Bargaining, Depression and Acceptance. So you may gather from that there is some angst involved. Post 'Chosen', Buffy and Spike
Normal Again by Richard Bachman
Summary: COMPLETED; based on the episode Normal Again. Instead of Buffy, Spike was poisoned by the demon and his consciousness was transported into an alternative reality where he found himself incarcerated in an asylum.
This one is all human.
Traveling Soldier by Zarrah
Summary: AU...SB...Based on the song 'Traveling Soldier'. Buffy meets William on his way to war. Share their growing love through letters. Come inside for the complete summery! Complete
Hope these help.