It wasn't exactly difficult to find out where Ambrose lived, in fact he had found out shortly after discovering that Buffy lived with him. It wasn't stalking really, just insurance for times such as these when he had to escort Buffy home for being a reckless child having a tantrum.
He pulled up outside of Ambrose's home and turned off the engine. Without further comment he got out of the car and moved around to let Buffy out.