Mrs. H, Blood is thicker than water when it comes to the inlaws. I would suggest that you not contact her for a while. If she opts to contact you, be friendly and do not share anything about what you are doing w/your life and do not discuss her son w/her. She's on the fence and doesn't know, nor most likely does she care what is right or wrong at this time. All she cares about is that her son is talking to her. I would also be careful how you deal w/his grandmother as well. These women are talking to one another and I wouldn't be at all surprised if grandmother tells her everything that you tell her, just in casual conversation. You can respect her at arm's length.
Continue to hit that delete button!
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.