Although it is easier said than done, I do not think you should be so hard on yourself for this one. Based on what you said and the mixed messages you received, it seems as if the girl you’re interested in may be confused about her feelings and/or is still reeling from her last break-up. And when people are confused about their feelings, it is usually an issue they have to work out by themselves. So, it doesn’t seem like anything you could have done would have made the situation much different or changed her mind. Although it may be difficult to do, if she has expressed to you that she is not interested, then that is something you have to accept. However, given that you have received mixed signals from her and her friend, perhaps you should talk to her, or her friend, about the situation. Finally, just remember, if she changed how she felt about you simply because you decided not to kiss her one time, then she may not be someone you want to be involved with in the first place.