Killing Willow hadn't been as hard as he had always thought it would be. Sure, they had been friends since forever and lovers since they were Turned, but in the end, that whole not having a soul thing made it pretty easy for him to take her out of the equation. Not having any kind of conscience totally rocked, that was all he had to say about it.
It was funny that he would be the one to survive even though this new life had started out with there being three of them--Xander, Willow, and Jesse. If he had honestly thought about it, picturing his human self in his mind, he would never have believed that he would have been the one to make it through. Yet here he was, way past that whole living in Sunnydale thing, traveling out and about in the wide and wonderful world.
He probably could have stayed in Sunnydale and ruled things with the typified iron-fist, but it just wasn't worth it. He hadn't wanted to deal with the trouble of telling the Master that not only had he allowed Angel to be ashed, but that he had killed Willow himself. He just so wasn't into the being punished lately. Torture had never been a fun thing for him, at least when he was on the receiving end. Giving it was a whole 'nother story.
So he stole a car and roared out of Sunnydale, driving around and exploring the wide wonder of the US of A for awhile, before that got boring and he headed across the ocean for some kind of foreign adventure. Which was how he ended up in Scotland just when things started to get interesting... and fun.