Would it help to join a support group or forum for people who have a similar issue in their past? It might help you move past the shame to really see that there are other good people who have made those mistakes. I realize you're asking for advice on how to give your letter to T but it sounds like you're just so terrified of being further shamed and judged. It might be healing to find an anonymous context in which you get to experience compassion and understanding from people who have been there.