The word 'bae' refers to one's girlfriend or boyfriend. It is a kind of shorthand or slang for the common endearment 'baby'.
The term "dude" may also have derived from the 18th-century word doodle.
The word 'sweetheart' was most likely first used in the 13th century, when it was first 'swete hert'.
The word 'endearment' originated from the 1620's, where it meant 'obligation of gratitude'. It wasn't originally an expression in romantic love.