Ambivalent, We all have been where you are today and have felt the same. It takes time to detach after being dealt a heavy hand of surprises. However, you are the only one who can stop your fears and make detaching work for you. It takes time, but you can do it.
Now, about your h and his statement about not coming for Thanksgiving. I can understand what he's saying. Yes, it's going to feel awkward for him. Why? Because he's doesn't feel comfortable doing the "family" thing right now because he doesn't know what he wants at the moment. He is in crisis and he's not feeling all that warm and fuzzy about family gatherings. It could very well make him feel uncomfortable. If he doesn't come, he may very well stay home, sit in a corner and just watch tv. It does not necessarily mean that he wants to spend the day w/ow.
You need to start focusing on your studies and prepping for your exams. You are spinning yourself up like a top and you have other things that require your attention right now. Keep the focus on those things that require your immediate attention.
It's difficult, I know, but you have to let him go. Allow God to work on him. The fear will go away when you face those things that make you fearful. You are going to be okay...but you need to face those fears head on and go from there.
Take care of yourself. Leave your h to twirl in the wind.
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.