obsessed(fixated on a single topic or emotion) adjective [UK: əb.ˈsest] [US: əb.ˈsest]
obstinate(adhering to an opinion, purpose, or course, usually unreasonably) adjective [UK: ˈɒb.stɪ.nət] [US: ˈɑːb.stə.nət]
stubborn(refusing to move or change one's opinion) adjective [UK: ˈstʌ.bən] [US: ˈstʌ.bərn]John is as stubborn as Mary. = John es tan obcecado como Mary.