Complex sentence: Meanwhile, Angel becomes convinced that Buffy's love for him will be bad for her in the long run; after the battle with the Mayor he leaves Sunnydale, leading to the spinoff series in Los Angeles.
Split into simpler sentences: Meanwhile, Angel becomes convinced that Buffy's love for him will be bad for her in the long run. After the battle with the Mayor, he leaves Sunnydale, leading to the spin-off series in Los Angeles.