Cat upset when boyfriend moves in

DEAR HARRIETTE: My boyfriend recently moved in with me, and ever since then, my cat’s behavior has completely changed. She’s been acting out: scratching furniture, hiding for hours and even refusing to eat sometimes. She used to be calm and affectionate, but now she seems anxious and territorial. My partner is trying to be patient, but I can tell he’s getting frustrated, especially since the cat hisses at him whenever he walks by or tries to sit near me.