Knowing how things work has always been helpful to me, so I'm going to share it in hopes that it will help you as well. You've lost a part of yourself when you broke up. You've invested yourself into being with her. Now that this part of yourself has been torn away from you, you feel naturally empty - and now that you're forced to meet with this part of yourself being inaccessible, you feel pain. It's normal: it means that you cared about this part of yourself, about the two of you that you had. dingus's already said it. Invest yourself into you: do something that channels your own mind and feelings. There's a vacuum of personality inside of you right now, and anything that puts some pressure onto you (as light as it may be - the pressure of wanting to play guitar good, to code well, to sing beautifully) will fill that vacuum once you let it in. Other things will just fall through. Make yourself feel whole again. Best of luck.