wear one's heart on one's sleeve

1. To express affection or sentiment too openly or ostentatiously: “You have to play it cool with a girl like Heidi; you mustn't wear your heart on your sleeve.”

Idioms and Phrases

Also, pin one's heart on one's sleeve. Openly show one's feelings, especially amorous ones. For example, You can't help but see how he feels about her; he wears his heart on his sleeve. This expression alludes to the former custom of tying a woman's favor to her lover's sleeve, thereby announcing their attachment. Shakespeare had it in Othello (1:1): “But I will wear my heart upon my sleeve for daws to peck at.”