Slang: Hung up on

Definition: To be obsessed about something or someone.
Example: 1) I'm really hung up on Samuel -- I can't get him out of my mind!
Etymology: If you are 'hung up' on something, you are caught and cannot move freely. 'Hung' is from 'hang', which means 'to attach from above' or 'to suspend'. So whatever you are hung up on, it has you on its hook, and you're swinging helplessly like a fish pulled from the ocean.