I can relate, Everydaystruggle33. I also find myself going back far more often than I'd like too. As well as having a crush that left me feeling very similar to what you've stated. She just loves using me for attention and when it's best for her convenience. It is entirely unhealthy and borderline addicting and you only walk away seeing these when you aren't infatuated or at peace of mind because they aren't around anymore. You did or said things that you later regret because your reality did not match how you thought/wanted it too. (The movie 500 days of summer comes to mind haha)
These emotions cloud our actions and judgement.
It's something you genuinely loved suddenly gone, missing, and you're longing for it again. Especially when it was something that changed your life and views completely. You just simply want someone to do the same for you. Sorry, I'm rambling cliche **** now lol.
I suppose it's different for everyone, and "logically speaking" moving on is the best route. However.....
In my opinion, there's are a few understandable exceptions to this and as to why it happens, and while it might sound as being self-justifised... What if you weren't given proper closure? The ex selflishly blames the other for everything? Naturally, you'd keep pushing and trying to prove that isn't the case. That's when you loved some one so much that you see them in the most non-cynical way possible that they are speaking the truth when they aren't.
Some people want to take the selfish coward way out of a relationship without the guilt, some take the honest route of saying they found someone else or fell out of love. The former will make the 2nd party a hell of a lot more likely to not be able to move on with ease and is entirely ****** up. But once you realize it, it should make it you realize how of much of an ******* or ***** that person was and truly gave no ***** about ya. Sorry for the language lol.
How someone "clings" or "stalks" onto a ex after the break up has other factors that should be considered. Who is anyone to pass judge on someone without knowing the story. There are very human responses to what people say or do. But that would require an already open minded person whom would realize that before even being selfishly coward or manipulative. Empathy shouldn't be selective, folks. But sadly, it is.