Richard Bach - in Illusions - wrote (or was it Shimoda?) "You are always free to change you mind and choose a different future, or a different past", later he adds, "If you will practice being fictional for a while, you will understand that fictional characters are sometimes more real than people with bodies and heartbeats."
So do not regret choices from the past, just make a new past. Worked for Mata Hari - well for a while anyway
R