Desire for a person is not the same thing as having that unique appreciation and need for them, nor is affection. Desire waxes and wanes, and affection can be felt without long-standing commitment. But 'You matter to me' means that the long haul is accepted, even willingly taken on: I will carry you, hold you and applaud you, from here on in. Dependability: I will be here to take care of you. And when you are gone, I will be here to remember you.