The sexual harassment that you mentioned was from the lady that was playing Alison's body double and it was from a few seasons back. It was in the media because she was bringing charges against Showtime. It was to do with the name that was written for her on a call sheet. There was no mention of Ruth in the media for this, as it was to do with her body double. That's all I could find on twitter, so I'm hoping correctly that this is what you are referring to. Somebody corrected them by saying it was Ruth's body double. Josh and Ruth never dated. Ruth cleared that up in quite a few interviews she gave at the time it was speculated.
Sarah didn't say why Ruth wanted to leave other than she asked to do so. Ruth has a lot of work on her plate right now, so it's possibly because of that. She recently was announced to be in a new tv series for the BBC. Plus she has the series about her grandmother, that you mentioned. These are the ones I know about and there could be others. Sarah has said great things about the next episode on twitter, so I don't think there is any animosity there from her.
This was a wonderful episode and I was sorry to see that this was how it ended for Alison. The writing was great and this writer will be writing more episodes in the future Sarah has said. The direction was also great and the director did a great job. Loved the Noah, Cole and Anton road trip and the humor was what was needed for the gut punch we got in the second half. It was a really well done and acted episode. It freshened my resolve to stick with this show because I was seriously wavering during much of this season.