How is having an unmet longing NOT painful? I'd love to figure out where the misunderstanding between the two sides is occurring.
Right now there's some pineapple in our refrigerator, which I'm going to snack on in a little while. I'm experiencing a desire for some of that pineapple, which I don't experience as a pain but as an anticipation of a future pleasure. Before that, however, I desire to take a nap; I'm experiencing this desire as a reaction to the pain caused by a bad night's sleep last night.
For me, desire is intricately tied to both pain and pleasure; it can have elements of either or both. My practical Epicurean take is that desire provides the stimulus to action, while pleasure/pain provides guidance in how to act. Practice involves being aware of and responsive to all of these: desire, pleasure, and pain.