She didn't notice anything was wrong, she didn't realize she wasn't in love with him, and he wasn't making that much effort to tell her he wasn't alright.
Yes, and whilst Riley isn't innocent in all this (He continued in a relationship because he hoped she WOULD love him), but Buffy SHOULD take some of the blame for the situation for the very reasons you list. This is her lover, her boyfriend, and she didn't notice when he vanished off for hours at a time with no explanation?
Vampires in Sunnydale meaning people getting killed in Sunnydale, I think we should cut Buffy some slack on doing the job she was Chosen for, no matter her motivation at the time of staking.
Hardly, she was not being a Slayer at that point, she was