More then just a friend?

No, I don't think that's wrong at all, at the end of the day, your ex as you said "ran me in the dirt", so even though nothing came of that relationship doesn't mean it has to say it was a complete waste of time. It sounds like her friend was into you while you were still with her friend anyway otherwise she wouldn't have made an effort to stay in touch and have dinner with you. If I were you I would go for it because the only harm it could do would make things awkward between you and your ex and at the end of the day, who cares, it's your happiness you need to worry about :) Hope this helps.