Just an observation, but this thread is in the S2 forum and the OP seems to be referring to when Buffy came BACK to Sunnydale after she'd had her social-life 'again'. So, although the OP refers to S1, to me it sounds like they're talking about S2, 'When She Was Bad'.
But, to keep the conversation going, I think Buffy's issues in S1 are the fact that her Slayer-ness forced her out of school, forced them to move to a small town in the middle of nowhere, which was the only place who would accept her after what she was forced to do.
In S2, however, I don't think it's the fact that she got her 'Cordelia-esque' lifestyle back, but more to do with the fact that she was able to be a normal teenager for a few months. She didn't do ANY Slaying when she was with her father, no patrolling, and she got to remember what it was like when she was a normal person, a normal teenage girl. But when she got back to Sunnydale, literally the second she stepped foot out the front door and went to look for her friends, she was shoved head first back into that life, she was back to being the Slayer. And not only that, but she still hadn't come to terms with the fact that she had fulfilled the prophecy of being the Slayer - she died. She never faced that, never dealt with it, just pushed it to the side to deal with the immediate problem - The Master - and then forgot about it to celebrate the fact that the world hadn't ended.
All of that added together made Buffy a very unhappy girl and she dealt with that by trying to push everyone away so that she couldn't hurt them.