Og Haley ded
Og haley committed suicide while Mason got a second chance at living for a purpose but because his body was already harmed enough it was switched with haley. If I'm not wrong it's specifically haley because Haley already met Noah and even asked him to sleep with him or wtv.
There's another manhwa called "Again (yaoi)" where the mc called Han Nokyoung commits suicide after he made another man commit suicide for telling him bad things or something and since his mother was a shaman he got a second chance at living but in his own body and he fixed his reputation even with a man called Mr. Kang. Its not EXACTLY like this manhwa but it definitely shares the same idea with a different start and a different ending
didn't really answer how they switched souls and where OG Hailey went but ok.