Of the two, who do I choose? Why does it have to be this complicated? What do I do?

My ex broke up with me because she was holding on to past hurts. She was so scared. She said she saw her ex in me. I set her free. Let her find herself. Now that she has found herself, and says she still has those feelings for me...I've already found someone else! And i can't break her heart! My new girlfriend told me I wasn't like the other guys. That I wasn't an *******... Tell me: How can I afford to break her heart?!? She said she found her Prince Charming on a white steed in me! I can't break her heart! But I still have feelings for my ex! And she still has feelings for me. I can see she was hurt when I told her about my new girl. I could see that. She apologized to me for finding herself too late. And that had things been different, she would've stayed with me. What do I do?!? Why does it all have to be so complicated?!?