The guy's name is Kaiden, and he is obsessed with you because he has an unhealthy attachment to you. His attachment issues stem from childhood trauma, and this attachment to you has taken control of his life. He is extremely possessive, controlling, and jealous, and will do anything to keep you from other people. He has a strong sense of entitlement towards you; he believes that you are his property, and he will treat you as such.

"You're Mine, no one can take you away from me."