"I bet" is usually used to indicate "I think it is probable." "He came in looking pretty bad. I bet he was drunk last night." "You bet" is used to indicate certainty - not something probable, something certain. "Will you be there on Saturday?" "You bet! I wouldn't miss it for the world."

#1. - I #2. - YOU That is the difference.

bet is a term used by the native speakers which means know or sure.....i is refering to yourself while you is refering to another party who u are talking to