Sufferer here. Numbness for me cannot be controled. When I am overwhelmed with emotions, I go numb. When someone is upset with me, it is not safe to feel so I go numb. If that person gets more upset I go more numb for longer. And I cannot control any of it. I certianly cannot offer a genuine hug in that time. If someone is like "hug me you asshole" it will be a forced, void of all emotion, hug.
I will then isolate or leave because its not safe around high emotions and when its not safe I flee for saftey. Then, when I unnumb I have a shit load of PTSD shit to deal with which is really not for supporters to see plus we want to protect you from all of that and from getting accidently hurt by us because of it.
Its rather predictable. It sucks and I am sorry that it sucks but at least you can predict it thus prepare yourself for it.
I would also maybe learn to not get upset when he does things that he likely cannot control (becoming numb) and cannot do (give you a hug when numb). Just 2 of the many things we cannot control and cannot do. It will make being a supporter 10 times easier. Not easy. Just easier.