You are asking me to tell you what you should do. It isn't my role to tell you what to do. That would be overstepping my bounds in a big way.
What I can do is help you understand the dynamics that have you blocked, and then you will feel freer to make a decision. My first question to you is why do you need someone else to tell you what to do? Why don't you allow yourself to make your own decisions?
I suspect that you are frozen because you feel guilty to dump your girlfriend. And, you seem to be thinking that if an authority tells you to do it, then you won't have to feel so guilty. But, our goal isn't to evade your feelings. You need to identify them and understand why they are occurring.
So, find out what is holding you to your current girlfriend. Fear of hurting her feelings or guilt? So ask yourself, 'Why don't I allow myself to follow my heart?'
I got the message in your letter that you would really like to date this girl that you are crushing over, if it weren't for this mysterious force inside you that has you frozen. As you search for the answer to the above question, go way back to your formative years and find out if someone gave you the message that you should put your feelings and needs behind those of others.
Perhaps you saw one of your parents actually placing others ahead of him or herself. Your next challenge will be to soften the harsh conscience that blocks you from following your true, inner voice. You must get to a place where you listen to what you truly want and need and see to it that you fulfill these needs as much as possible.
If and when you decide to break up, then you must do so through a dialogue. You need to tell your girlfriend what isn't working for you. Protect her ego by talking about yourself.
For example, 'This relationship isn't working for me' or 'We have irreconcilable differences.' Neutral words and phrases in which you say 'we', 'us' or 'the relationship' takes the focus off of her and makes the break up pill easier for her to swallow. At all costs avoid blaming her by saying, 'You don't do this 'or 'You can't give me that.'
The word you is an ego killer and you want to allow this girl to leave the relationship with her self in tact. So put the blame on a faulty mix of personalities, not on her. I hope that this letter has given you what you need.