I had this happen with one of my first pair of boys, years ago. There was some loud noise while I was holding him, and suddenly we were back to square one. It's probably nothing you did, but something spooked him. Don't worry, it won't take months again. But you do have to back up a few steps and work on whatever earlier step he's comfortable with now, then move forward. Once he sees there's nothing to fear, he'll progress quickly. I'm sorry, I know that's frustrating, but be patient and soon he'll be cuddling with you.