Hard, the only ones I come up with are ones where they were friends/close as children/youth, got separated somehow by hardships, then reunited again by fate as adults...if you want to try, they are below. If not, no prob. :)
Spring Waltz (melo)
My Little Bride (youth/adult mix)
Delightful Girl, Choon Yang (youth/adult mix)
Summer's Desire (melo)