Its so like when you rub a perfume on your skin. It takes a while to stay and then amalgamates into your skin until it becomes a part of you, giving you the most pleasurable, soothing feeling. Though its lifetime is short and somehow it has to fade away but still it makes you addicted and you tend to go back to it over and over again.
This you can relate so comfortably to a person who comes within your range of attraction, touches your heart with that unpredictable intensity, stays a while until is absorbed into your blood and becomes a part of you. Though even at that time you know, they would have to eventually go, you become addicted to the charms. Like a perfume they may give you pleasure and may sooth your nerves but their fading away brings about these withdrawal symptoms. You may or may not have a chance to go back to them, yet the longing persists.