I confess that I do not understand a person’s psyche. That “thing” unique to each of us. With time I can understand why someone does something, how their upbringing, education and sphere of friends influences their decisions and actions. Still I want to believe that there is something else, something singular to each one of us which factors in to our actions.
What causes one to start an electronic conversation with another then suddenly disappear mid-conversation without even a “goodbye” or “I need to go” and think nothing about apologizing later?
Livedinitaly's Blog 
This is so relatable. I have often wondered about the abruptness of such a thing. And still wonder.
Rudeness? Lack of manners? I do try to say when I need to leave a chat and if I can’t for some reason I do apologise later. It’s just about being considerate and consistent. You’d never dream of simply walking away from a RL conversation without saying goodbye.
Maybe, and I hate to put this in to words, what they actually think of your relationship with them.
Disposable?
I see disposable as a one-time use. This has happened multiple times and each time it is brushed off as nothing of importance. Maybe it is time to say goodbye to them?
Perhaps… They obviously aren’t as invested as you are. Or they don’t care that you find it hurtful. Shows a lack of respect for your needs I think?