It sounds like you were very much inlove with this girl and that you are now heartbroken. It's not surprising that its taking you a long time to move on, don't add to your woes by beating yourself up over your feelings, take them each day as they come and over time you will find things easier to accept.
That said, I'm afraid I do have another piece of advice which may sound harsh. You must stop looking at this relationship through rose tinted glasses. Though you feel it to be the case you have to realise that this girl was evidently not perfect for you in every way. If she was she wouldn't have desired breaking up with you and breaking your heart. Likewise, evidently you were not perfect for her in every way, if you had been she would not have left you. I am sorry if my bluntness causes you distress, but you are doing yourself more harm than good by constantly thinking about how great you had it back then. Constantly referring to the past and how wonderful it was will not help you in creating a happy present.
Don't worry that you don't feel ready for other relationships, worrying over it is only putting extra pressure on yourself. It doesn't matter that you're not interested in other women, what matters is that you start trying to enjoy your own life as it is now, as a single man. Grieve for your lost love certainly, but do other things aswell. Go out with friends (not to meet women, just to have a good time), start doing things you enjoy doing, sports? Arts? Anything at all. It sounds to me that you just need to concentrate on yourself, do things for your own pleasure, build up your confidence and then you will find moving on becomes easier.
I don't mean to trivialise your feelings by suggesting it's as simple as stopping thinking about her and being sad and starting to think about yourself and being happy, I know it's not that easy to do and it will be a slow progression, but you must, for your own sake start trying.