He meant Guld, and there's never any proof as to Guld being a rapist, all that's shown is a raged outburst & ripping Myungs clothes. After that (given by what little is shown) I'd say he looked in the mirror, freaked out, blacked out, and completely jumpled events in his head, believing that Myung couldn't have possibly chosen Isamu over him, and that Isamu must have been raping her.