If you want to be with this person for the long-term, I have two pieces of advice for you to consider.
First, I agree with @DarkestKnight that obsession is rarely a good solution. Check out this thread if you want to see how things can go with obsession spells. A better approach would be to encourage genuine passion to develop between the two of you. While passion is a powerful emotion, it is not all-consuming in the way that obsession is. Passion allows for space and honesty, while obsession leads to burnout and unrealistic fantasy.
Second, I find your end goal of breaking her heart to be strange. If you don’t want to be with her forever, that is fine, and there is no need to encourage the development of those feelings between the two of you.
I think it is important to remember that magick has an effect on you, the user, as well. Whether it be for money or for love, you will be influenced by the spirits that you call and the results that you receive. If you do magick to have a partner fall in love with you, it would be naïve to assume that this would not change you as well. You may very well find that her heart is not the only one that becomes broken.
Whatever you choose to do, spending your time worrying about the results will not help you. Lust for result is a common challenge among occultists, and one effective solution is to recall the feelings you had in the ritual associated with your end result. Remember that you performed magick, relish in the power, and then get on with your life. Results will come, in time.