DP and I recently got married after years together. His elderly DF who is a widower has asked me if I would call him Dad in future, now that we are legally married. My own DF died when I was young, I was close to him, and miss him still, and I don't feel comfortable with calling anyone else Dad, even though FIL is a nice man who has always been kind to me. AIBU if I say I would prefer to go on calling him by his first name. Would appreciate views on this. Thanks.