Student or Learner
What does the sentence "If Scott wanted to keep his life secret, that was fine by her" mean? Does "keep his life secret" here mean "keep his life a secret" or "keep his lifelong secret"?
I probably means that he he wanted to keep his life a secret from her. That is, that he didn't want her to know what he was doing (or who he was doing!).
It is possible, determined only from more of the context than you have provided, that he did have a "Life Secret" but I doubt it. The only person I've met (and I did meet her!) who talks of a Life Secret is Oprah.