Imagine if he had just muster up the courage to properly look her in the eyes and clear his name, they wouldn't be in this mess, avoided all of the tragedy.
Reading the epilogue, maybe he did have the courage to say it but once the saw the evidence (panties) planted in his bag, he thought how's he gonna prove it when the odds are stacked against him like this, who would believe him? Especially the the victim who's doubting him now. Or he's just nervous and unassertive