Hello Silgi,
You say you've never experienced deep love before this occasion and that she made you feel very good.
Well, I'm sorry to say, like the others, that this doesn't sound like deep love at all. Maybe it will help you to read
this description of love.
What you describe seems to be more related to what we do when we're trying to satisfy our unresolved childhood needs with relationships. It's very common and it happens on different degrees. It sounds as if she was trying to play out the dynamics to which she's used to, and part of that is probably having a relationship that never really gets too serious (even if she was 'dreaming about a wedding). She'd probably stop 'loving' you so much once she had you all for herself. And you have your own responsibility there because it takes two people to play these dynamics. You probably have an unresolved need for validation or something along those lines which made you go for someone who was idealizing you (for her own benefit) and that made you feel good, which you confused with love. It isn't love, it's all about feel-good chemicals that make you believe that it is true love.
The problem is that you also seem to be OK with the fact that this dynamic is a bit of a toxic dynamic, even hoping that things could change in the future. They most probably won't, and that's really part of the recipe for toxic relationships: to go there with all the signs that it isn't good and yet ignoring the signs and hoping that one day things will go better. 'If I love her, she'll get better', 'if I leave my wife, she'll get better', 'if we get married, she'll get better'... all when she hasn't shown you a sign that she really wants to be better. And that's the thing, she'll only be able to get over her issues if she really wants to do it, and you have nothing to do with it, it's not your business now. So you need to focus on how YOU can be better yourself, if you are willing to do that, of course.
Now, about the obsession. It's also very common in these dynamics to feel obsessed. It actually is another sign of a toxic dynamic. And there's no way out if you don't want the way out. With any obsession, be it a drug, another type of addiction, or a relationship, you have to make a clear decision of letting it go for it to 'go away'. For that, you need to be convinced yourself that this wasn't good for you and that it's better to move on and leave this obsession behind. If you are convinced of that, then you can write all your reasons for that and work on reminding yourself of those reasons everytime you feel the obsession coming up again. It will take time and work, and it won't just be erased either, but that's a good thing if you're learning from this experience. The memory of what happened without the obsession can become the lesson you learn from it and what makes you grow up.
You can do it, if you really want to do it.