1. Richard has never made a secret of his love for Jane. He has always worn his heart on his sleeve.
2. If you want to attract someone, sometimes you have to pretend you don’t really care rather than wearing your heart on your sleeve.

The expression suggests that a person’s heart (and therefore feelings) is exposed for all to see as though it were worn on the sleeve. In medieval Europe, knights used to tie to their sleeves handkerchiefs or ribbons representing the women they loved. In the 1700s, young men would wear the names of their sweethearts on their sleeves for Valentine’s Day.