Usually when we are 'stuck' on another person it is because they are showing us a part of ourselves that we are denying. This doesn't mean that you are a cheater and are denying it, but it is time to ask yourself what behavior you saw in this relationship ( from her) that may be something that is a characture of your behavior. Often times this can be something like you finding yourself in a reverse role, or finding yourself in the exact same role, different girl.
My suggestion is that you look at the relationship BEFORE this one and see how the roles are a little reversed,( or not) not quite as obvious, like you never really CHEATED on her, you just weren't really into her ( or maybe she wasn't really into you?)….and may have thought of someone else? Anything along those typse of lines, then you will find WHY you are creating a situation where you are unhappy with the the treatment someone else is giving you, and you find yourself wanting MORE of that.
These situations come up not so you learn to live with them, but so you decide what you need to change in you to have a relationship that you want, it may be something as simple as focusing on a different type of person all together to actually changing what your expectations of a relationship is - remember that the only expectations most of us have of a relationship is what was taught to us by our parents, and just because your mom was bad at relationships does not curse you to that same issue your whole life.
Look inside yourself, doesn't that person you see deserve to be treated as good as you want to treat others? Don't ever forget that…. No one will ever treat you better than you treat yourself, and very few will ever treat you better than you treat them…
It's your choice how long you take to learn the lesson, those of us that like to deny ourselves take longer- maybe you won't….