You are doing wonderfully! You didn't freak out when he said he was coming to get the rest of his stuff...and knowing his patterns, he may or may not come and get it. Be prepared for either.
Do you like SIL? If so, go to her party! Make it about her...not H. Take the kids and get her a nice present.... If you don't like her...then pass on the party.
Do you have any platonic male friends? Could you find one to go to the bowl game with you? I would. Or better yet, can you get a few friends to go with you...dress nice, go in a group, and have fun without H.
I'd call the brother's house on Thanksgiving and wish all a happy day. Then you'll know for sure whether folks are there or not and yet, it appears innocent enough to want to wish family a happy holiday.
Let him watch the little guy while you hunt. It's the least he can do...and you have a great time hunting. Do you have friends to go with you? Take them! Get home late...take a change of clothes and show up to pick up little guy looking great...casually mention stopping for a few drinks or dinner out after hunting with friends.
Do not let him see you upset! If he asks if you even care that he is getting stuff out...say of course you do, but you can't do anything about it. Tell him you love him, but realize he has to do what he has to do. Tell him you haven't given up on the marriage, but that you want him to be happy.
Now, here's the joke I am telling all today....for a giggle..you can change the mother in law to OW or whoever else you'd like to put in the second hearse... A woman was leaving a convenience store with her morning coffee when she noticed a most unusual funeral procession approaching the nearby cemetery. A long black hearse was followed by a second long black hearse about 50 feet behind the first one. Behind the second hearse was a solitary woman walking a pit bull on a leash. Behind her, a short distance back, were about 200 women walking single file. The woman couldn't stand her curiosity. She respectfully approached the woman walking the dog and said, "I am so sorry for your loss, and I know now is a bad time to disturb you, but I've never seen a funeral like this. Whose funeral is it?" The woman walking the dog replied, "My husband's." At which time she was asked, "What happened to him?" The woman replied, "My dog attacked and killed him." She than was asked, "Well, who is in the second hearse?" The woman answered, "My mother-in-law. She was trying to help my husband when the dog turned on her." A poignant and thoughtful moment of silence passed between the two women when the woman was than asked, "Can I borrow the dog?" "Get in line."