Dear Prudence Prudie chats with Lizzie O’Leary, host of What Next: TBD, about an unwanted blast from the past in the middle of a wedding. Photo illustration by Slate. Photo by Daniel de la Hoz/Getty Images Plus.  Each week, exclusively for Slate Plus members , Prudie discusses a new letter with a fellow Slate colleague. Have a question for Prudie? Submit it here . Dear Prudence, My 25-year-old daughter “Anna” is getting married in June, and I just found out something terrible I thought I’d left safely in the past. Fifteen years ago, I cheated on my wife. We’d been having a lot of issues getting along and I slept with a co-worker, “Jenny,” who was about to move away due to her husband getting a better-paying job out of state. I assumed it would be a one-off thing, and my wife would never find out. Thing is, we ended up hitting it off so well that she would fly in to see me several times a year, and I would fly over to where she was.…