Hi Mleigh- out of curiosity, what do you guys normally do for Thanksgiving? Do you see extended family or do you keep it small? Are you going to do the same thing just w/o him or are you going to do something completely different? The only thing I am thinking is, what if H suggests dividing the day w/ S when you try to do something separate from him?
Our sitches are kind of similar in that there is still a lot of contact with spouses. I am sure my H would want to see our kids part of the day. In fact, he might have asked why I would have them and he wouldn't. Just a thought.
In addition to all of Sotto's great advice, if there are times it's sort of assumed that you all might do something together, I would make plans during that time. So, if Saturday afternoons he usually wants to do something (Costco lol) I would make plans then. But he will ask your son where you guys went. I am sure. This is what my H did. He would text my son and ask where we were and what we were doing. Your son is a little young for texting maybe, but H will be on a fact finding mission when things start to change.
So if there is a time where H has s and he invites you to hang with them, those are the times I think you should make other plans. He may ask you where you went/what you did or he may probe your son later. Just my .02.
Me 41, H 47, M 15 yrs, S11, S13 BD 1: 11/4/14 we work on it; really I pretzel myself BD 2: 3/31/15 H goes down to "dorm room" 8/15: H back to MBR 10/15: H back in dorm room 1/18: H files, now divorced