If you decide to ask him if he saw your and your mother's message on the other group, I would phrase it as "h, btw, I was wondering if you happened to see our messages on xxx group?
However, I think I would wait on asking him for a bit. You don't want to appear to anxious and/or needy in responding too quickly. By responding quickly, it tells him that you are sitting around waiting on him to contact you and that you are still Plan B in his mind. Give it a day or so and then respond back, but keep your questions very simple and give him the opportunity to feel like he can respond or not.
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.
