The stress is from being on the fence
Imagine yourself standing, teeter-tottering, on a fence, afraid to jump onto one side or the other. The fear and anxiety is enormous, because the perceived imaginations of what would happen if you jumped on the wrong side is unimaginable. This will kill you - stress kills, and you will have this stress for as long as you stay on the fence.
You must settle it one way or the other. If you stay with him, it must be settled that whatever necessary, you will be happy, try to make him happy, and make a wonderful home for your son. If you decide to separate, do so, without looking back and agonizing over it, still trying to make a wonderful life for your son. With either commitment, you can make a length of time that you will try it, and stay committed to that length of time. This will give you more clarity. For instance, you can say, OK, I will fully commit for the next two year. I will give it everything I have. I will try 150%. I will smile when I want to cry. I will love him unconditionally. I will do it and be consistent, consistent, consistent. I will do this and know that if I do have to separate after two years, the breakup will not be from anything I have not done. Or you can take a separation for a period of time, perhaps on the excuse that your son needs more stability. If you could be around your family or some source of support, that would be helpful. Your husband will have open access to your son, and it will be something you will encourage, but not something you agonize over, trying to make it work.
You will have your stress as long as you stay in one situation and wonder if you are making the wrong choice. My mother stayed with my father for the "sake of the children" and I grew up in a dysfunctional home with much turmoil. I divorced my husband so my son would not grow up in that kind of home and he is the sanest, most emotionally stable, wonderful man - the first "normal" non-dysfunctional person in our family, I think. So you can see why I cannot recommend you stay on the fence, raising your child in a dysfunctional home, wanting to keep the family together at all costs, but those costs right now seeming to be very high, and while you think they are costing only you, they are and will cost your son. But you have to decide, either permanently, or for a certain length of time, to get off the fence.
Good luck. Peace to you and your family.