Why does Lily not tell August about her life before, why does she lie?

Lily lied about everything to August and her two sisters from the beginning. Later in the book she would still not tell anything about her past. I think she does this because she does not want them to know who she really is. She is afraid that if they no about her real life they will not like her. Lily is still regreting her past. August even knows that Lily is keeping something big out. I think that Lily should have told them from the beginning because they are nice woman. I think they would have still accepted her. Lily just needed to put the past behind her and live in the future.