Well, it seems like maybe it wasn't entirely a bad weekend. I would say it seems like he's sending you some signals that he wants change. That's a good thing, I think. However, you're right to take your time and think about it. I know everyone is different, but the problem with my W and I is that as soon as we would decide to make things work it was like "Mission Accomplished" and we'd just fall back into the same habits that caused the marriage to break down in the first place.
I will caution you on dealing with his mother, particularly through email. As his ex-OW proved anything that goes into email can linger on longer than the feelings that inspired them. Also, you have to remember, no matter how much they care you, his family will most likely view things in his favor. So if she was telling you to get a D it's only because she believes that it is what he wants. However, just because she thinks that does not mean that it really is what he wants. People tend to say things in the heat of the moment or to manipulate the emotions of others, not realizing that people you say those things to aren't always able to know your true feelings. The fact that he seems to waver so much would lead me to believe that he doesn't really know what he wants either.
Keep focusing on the positives and don't let the negatives weigh you down.
