Sounds like trauma bonding.
You see when the are around there's lots of ups and downs and your body gets conditioned to that. They are a sort of framework for your emotions. If you keep them appeased, you have a quiet life...but if you don't...
The point is, when they are gone, you don't have that framework anymore. Your emotions and hormones like cortisol go into free fall.
Which is mad. It's like, looking for the cause of your anxiety - to cure your anxiety. That's why you may feel really panic stricken at the thought of him leaving. But it's largely mental and hormonal conditioning. Once his is gone, if you cut contact to bare minimum and ride it out, it will settle.
Your body just needs time to realise there isn't a threat about 24/7. And mentally, you need time away from him to get out of the fog he has trapped you in.
Studies have shown that abuse not only damages our mental health but also, our physical health. Of course if you are told 'you have a problem', 'nothing you do is good enough', and that you are wrong or bad all the time, you will internalise that. And those thoughts will make you miserable. And that can make you sick.
Unfortunately, you need to pull out the knife in order to heal. And you need to do thar whilst the knife is still firmly impeded. Because it's not coming out otherwise.
Only in leaving will you find your clarity. You will not find it fully until you do. Trauma bonds hurt. But they are just addictions that we need to break.