You are obsessing. You probably obsess about other things too. You need to realize when obsession is providing a positive force in your life and when it is providing a negative influence.
I'm assuming that you do not have the relationship with this lady, that you desire. I also suspect that if you were to start developing are relationship that is approaching what you desire, it will NOT be like you are imagining it.
My advice is simple, just like me, "Let her go". Accept that you can create all that you need in your life, entirely by yourself. Become complete onto and within yourself.
Oh, happiness is an attitude not a set of conditions. You choose to be happy or not. Happiness like anger is a choice and not the outcome of things.
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The above advice is not provided by a trained individual and should be taken with scepticism, especially since I'm guessing about a situation and two people from a single paragraph.
Good luck,
Iam2 
