Affection is different -- it is completely controllable and directable. Affection is a positive feeling that someone else creates in you. If someone does something nice for/to you, that creates affection in you, and if they do something that gives you negative feelings, that destroys the affection they've created in you. You cannot create true affection for someone else within yourself, although you can pretend that it is there when it is not. And you cannot always create affection in someone else, because if they like, they can block it out. The only way affection can be created is if one person creates it in another, who allows them to do so.
A healthy deep relationship needs both love and affection. Love, which motivates us to create the relationship in the first place, and motivates us to work through the low-affection times. And affection, to fuel the relationship and nourish both people. A relationship can continue for a time with an imbalance of affection, but that imbalance itself is an affection-destroyer, so if left unchecked it will eventually bring the relationship to a halt.
In my relationship with my partner, we've always had love for each other, but affection has waxed and waned. For the first year of our marriage, I created a TON of affection in zir, and ze created some in me. The second year, I was going through intense counseling for the sexual abuse I went through as a child, and I had little to no energy to spend on him, so that year ze created affection in me and I did not create it in zir. But ze had so much left from the year before that it carried zir through (though it was draining on both of us). Then the third year I began creating affection in zir again, but ze stopped, for the most part. The affection ze had created in me slowly dwindled over that year until this January, I had completely run out, and I felt no affection for zir at all. That terrified me because I thought affection and love were the same thing, and I thought that it would be a permanent state -- but ze convinced me it wouldn't be permanent, and we began making changes. After a ton of work removing all kinds of problems that destroyed affection, we began to create affection in each other again and now I feel more affectionate toward zir than I ever have before. And I feel more confident in it because we have conquered so many affection-destroying habits. Nowadays, we're pretty good at creating affection and keeping it! Which allows us to realize love on deeper and deeper levels. ♥
I realize all of this might sound a little too... structured. I don't see love or affection as an equation, I assure you! It is still inexplicable magic to me at the same time. ;-)