A 32-year-old woman presents to the psychiatry clinic with her husband, who reports that she has become increasingly suspicious of his fidelity over the past 3 years despite no evidence of infidelity. She frequently checks his phone, questions his whereabouts, and has accused him of having affairs with her friends and colleagues. She is preoccupied with these suspicions and has lost trust in several relationships. She denies hallucinations or delusions unrelated to infidelity. Her mood is euthymic, and she has no history of mood episodes. She works as an accountant and maintains her job performance. What is the most likely diagnosis?