What would you do if a younger female family member told you that your bf of 3yrs touched them inappropriately?

The family member (Julia) that was touched is ually active and a minor,now it is known through the family that Julia has a strong ual appetite with both females and males but Julia didn't lead him (Mark) on or anything.Julia has already told her parents and the gf (Cindy) is breaking up with Mark.Cindy has already told Mark's mom about the situation and she is very upset with her son,what else do you think the Cindy should do.Now Cindy loves Julia and she loves Mark,but if Mark had the audacity to touch Julia in a provocative way then Cindy should do more right.Mark even went as far to show Julia a ographic disc as if he wanted to get her in the mood.Mark didn't completely fess up to it at first but then confessed to some of it but not all.And like I said Cindy loves Mark but also wants him to suffer,its a complicated situation,she hates him in the same breath but wants this to all go away in the same.I can feel her pain but have no answer so what should she do.Let me know if u need more info.