You did miss something, homey. It's not that she didn't want to be in a relationship, it's that she didn't want to be in a relationship with you. It's the same thing men do to women all the time. And word to Big Bird, unless you all mutually agreed to be together, you all were never together, no matter if you met every ancestor she's ever had and her mother calls you three times a week and every Sunday.
I wouldn't feel to badly about it. She would probably have cheated on you if you two were official. I'd bet all the money in your pockets that her current boyfriend was in the picture when you two were dating.
Very few women do not want to be in a relationship with somebody who loves and cares for them. So if you hear a woman say this, you should know that it means she's not going to be with you for the long term. It might suck to hear, but at least she's being honest-ish. She gave you all the info you needed to make an informed decision. She told you she didn't want to be in one because you said you did. I probably would have lumped her into jump off territory and kept it moving while found a woman to love who'd love me back.
Either way, she did you a favor. Now you're free to find somebody who wants what you want. Go forth and find love.