/Wǒ guānxīn nǐ/
I CARE ABOUT YOU, I AM CONCERNED ABOUT YOU
关 /guān/ is a part of the word 关系 /guānxi/ A RELATIONSHIP
心 /xīn/ is A HEART
TO CARE about someone is to have our mind (HEART) linked, connected, “relationshiped”, to the HEART of someone else.