to be fond of, to love, to be respectful of
忯 centers on a warm, positive regard: being fond of someone, loving them, or holding them in respectful esteem.
忯 combines the heart radical 忄 with 氏, which likely contributes a phonetic element. The exact historical development is uncertain, but the heart component points to an emotion-related meaning.
The heart radical 忄 beside 氏 suggests a feeling directed toward a clan or family (氏 can mean clan). Imagine a heart full of fondness and respect for one's own clan.
For キ, picture a key to someone's heart: key -> キ, and that key opens the door to fondness and love.