Complex sentence: His "newly changed" personality comes as somewhat of an unpleasant surprise, and he alienates his friends-the person they knew as fun-loving and quick to anger is now staid, slow to anger, and often unintentionally insulting.
Split into simpler sentences: His "newly changed" personality comes as somewhat of an unpleasant surprise, and he alienates his friends. The person they knew as fun-loving and quick to anger is now staid, slow to anger, and often unintentionally insulting.