Dewey, I feel your words. I was a couple of times in the relationships that ended the way you describe. I was betrayed, and it hurted as hell. I was cursing and blaming myself for my stupidity. These persons GOT WHAT THEY WANTED AND LEFT ME TO BE SOME WEAK, UNABLE, AND PRIMITIVE HUMAN CAPABLE OF PROBABLY ANYTHING BUT LIVING A FULL LIFE MADE BY MYSELF.
Now on the question of the criteria. You can understand that you will never be caught in the unhealhty webs created by your interaction with the one who manipulates you if only you won't try to control them. This is my opinion only. However, to my mind, one can have a clearly articulated tendency to control others who seem weaker in some respects visible to the one. At some point of time, the one might realize that what he is doing for another one is A WAY OF CONTROLLING, EVEN BY HELPING, SUPPORTING, FINANCIALLY OR EMOTIONALLY, OR IN DIFFERENT KINDS. Then, in my experience (of the 22 years of life), you can start to blame yourself for your exaggerated efforts to find someone who seems to be perfectly in need of your HELP. Nonetheless, what you can do is control by helping first and then trying to stop this. If you indeed like to control, albeit unconsciously, you are in danger of finding yourself in the trap of your own power directed towards yourself.
I've had such situations, and are careful to not harm anyone even by making enormous efforts to do something seemingly harmless, and ending in trying to leave the person (who can easily, and perceptibly, be sensitive to other's personal power) when the situation seems totally out of (your!) control. So, you may not do this at all.
Hope this helps.