It won't be a happy arranged marriage, that's for sure. Orva's mother obviously would hate cheaters, but seeing how Orva is pulling off stunts like this, it's possible his mother is actually spoiling him. It also happens a mother is exceedingly strict and merciless with others, but her own children, especially sons, could never do anything wrong in her eyes.
We have already seen it in Sandra's thoughts and words that Orva keeps avoiding his responsibilities and breaking promises like it's nobody's business. Maybe in the past it was more about escaping everything else to do sword training. That would still be easier for Sandra to accept, as it's basically harmless aside from being annoying for her. But now training has been replaced by spending time with another woman.