Idealization is only one of the many factors that hinders someone's obsession from leaving. I remember countless nights where I would stay up fantasizing about a former romantic interest, then plot about how I'd get them back into my life. Only to realize why we had stopped the connection from further developing--the reality of them.
I've seen this predicament occur with other people as well. I'll have a coffee with a good friend, and I watch as they idealize their former flames, then promptly stare down at their last messages with each other. It's easy to remember all the good times, and their ideal qualities--but this is ultimate disaster, and a great defense mechanism to cover up the pain of reality.
My ex just died. We weren't officially together, but we'll call him that for simplicity. He committed suicide, and as much as I hate to say this about a dead person--he was such a shitty person. To give you an idea as to how shitty he was--he was Hitler reincarnated. (He was Austrian too, which was ironic). Anyways, so reasons for committing suicide were many. To say he was a shitty person is a complete understatement. Sometimes I sit there and idealize him, then go on talking about his ideal traits. I really idealized his intellect, his career as a scientist, how vulnerable he seemed, and just how gentle he was..
However, if you exclude all those things from the equation, what do you have? Well, you'd have someone who enjoyed triggering suicidal feelings within me, bringing me down on every level, racist, wanted to burn down the world (something Hitler said), hated everything and didn't care about anyone but himself. Yes, I realize I can be hypocritical however, I'm nothing like him--I still have a heart, among other dark secrets I discovered upon his death. He didn't. He died alone because he was a piece of shit. Simple.
It isn't so simple, because these idealizations help keep the memory of the person alive. It's most likely the person you're obsessed with isn't as bad as a person as the scientist I mentioned. So here's what you do:
Write down all your idealizations of the person. Then, take them away. Who are they now that you've taken away these idealizations? Do you still like them? Idealizations work quite well with obsession, because they tend to feed each other. As one feeds another, it grows--and stronger.
Here are two personal examples to help you out:
My ideals of him
He was this intelligent scientist flying from Europe, on some work trip and it was "coincidentally" in my city. A lot of people romanticize a foreign romance, and I was one of those people. I didn't find his look particularly.. nice. He was this tall skinny Austrian guy, balding in the front. But there was something about how sensitive he was, and vulnerable he was. He tried to hide it well though. If I didn't see his true colours--I would've believed he was a calm, cool, collected guy.
The reality of him?
Surfer guy from Hawai'i:
He was this hot guy who saved me while I was stuck in the middle of a zip line. Additionally, with the romantic backdrop of Hawai'i and two young lovers on the beach getting to know each other, is enough to make anyone idealize the other person. There was nothing else I romanticized about him other than the fact that he was extremely hot.
The reality of him:
To conclude, I'm going to emphasize AGAIN:
Write down all your idealizations of the person. Then, take them away. Who are they now that you've taken away these idealizations? Do you still like them?
Watch all your dreamy fantasies about them break down as soon as you continually remind yourself of who they are.