Why do 你 think 天使 didn't stay with Buffy in the 7th season of Buffy the Vampire slayer when they were fighting the first, even though he was supposed to be the one to wear the amulet.

It is revealed in the spin off 显示 Angel, that 天使 himself was supposed to wear the amulet. However he gave it to Buffy saying that he wasn't the one who was supposed to wear it (and Spike ended up wearing it). Why do 你 think 天使 did that? Did he even 爱情 Buffy anymore- he sure got over her death quickly when she died in season 5 of Buffy the Vampire Slayer?