Why does Gatsby choose to confess his past in Chapter 8?

From the text, we can infer that the accident, Daisy, and all of Gatsby's dreams have fallen apart. The past he made for himself no longer matters, it seems to ne that he is almost relieved to share the truth.

It was this night that he told me the strange story of his youth with Dan Cody—told it to me because ‘Jay Gatsby’ had broken up like glass against Tom’s hard malice and the long secret extravaganza was played out. I think that he would have acknowledged anything, now, without reserve, but he wanted to talk about Daisy.