SOLVED. One word title "S..." man & woman combine into one [s]

[Christina]

Trying to find title for a book I read in 2011. It was pretty new then. It has an all black cover with tan-ish outlines of skulls/demons. A boy runs away from home and meets a man and woman who in the end meet and find out theyre part of the same person amd basically combine into one.

[Raz]

Clive Barker's Sacrament.

[Christina]

Thank you!!!