To open one's heart to someone — to confide one's true feelings and be openhearted toward another person.
彼女はやっと親友に心を開き、悩みを話した。
She finally opened up to her close friend and talked about her troubles.
初対面では心を開くのが難しい場合もある。
It can be difficult to open up to someone you meet for the first time.
カウンセリングを受けると、少しずつ心を開けるようになることが多い。
When receiving counseling, people often gradually become able to open up.