You must be feeling alone now without her, but realize this, you were someone before you met her and began dating her. Putting all who you are in a relationship always spells disaster. No one should be that important that you place all of who you are, and once were into someone else. No one can make you happy, that falls solely on your shoulders.
Rekindle the dreams you once had, and the hobbies. Perhaps writing your feelings down on paper, along with goals and the cons and pros of breaking up.
It sounds like you need a much needed break from life, and use this time to get to know you again. Be stronger for the next person you get involved with so that you do not loose a part of you again. Your parnter should compliment you, not carry you. They should not be a trophy or bling on your arm. Together you both accentuate the good qualities you share both together and singularily. The next girl is waiting around the corner of the turning point of your life.
Perhaps talking to someone professional, if you have had these feelings for quite some time, make sure you are getting enough sleep, and eating healthily to keep your mind alert and focused.
Don’t beat yourself up about the break up, you must have valid reasons, don’t second guess yourself now, often times the first choice is the right choice.
Your friend, Shannon