Promise Under the Cherry Blossom Tree

He and she have been childhood sweethearts since childhood. They made a promise under the cherry blossom tree: "We will be friends forever." After growing up - she and he still haven't forgotten the promise they made. But... They obviously like each other, but... They don't say it out loud. Can I really just bury this relationship in my own cherry blossom tree? This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.