You’re doing very well in understanding the psycho-dynamics. I agree that the abandonment was brought with you into this life and has manifested with your husband and now your son. Also, it's excellent that you are aware that you tend towards an addictive relationship with your son. You project your feelings of abandonment on him, and then become attached / addicted to him in order to resolve the feelings. This is the first step of becoming aware of your deeper feelings and then taking responsibility for them.
After you have a good day of creating art, next day you rebound into the negative. This happens because most of us are still operating on an emotional dualistic level. Our good feelings tend to get balanced by the negative, and if we are deluded into thinking that all we need to do is totally immerse ourselves in any practice that seems to lift us up, and if we become addicted to that practice, we tend to strongly create the negative rebound experience. The way out is to make sure you're not escaping into the art, or using it to suppress the negative, and then just welcome the negative as part of the total experience. As you process both sides, you transcend, which is the goal. I talk about this more in my book 'Emotion and Art.'
Yes, the left side of the body corresponds to the right brain.
Not sure what you mean by 'pain and openness.' Maybe I already answered that.
As you work on yourself, you affect everyone who is close to you. There is usually an unconscious dependant energetic alignment between people that maintains any relationship. As you heal yourself, the other person is no longer able to perceive you the same way, and their attitude towards you is forced to change as well. But this doesn’t mean the other person is necessarily healed. Suppose your son has an unconscious tendency to be attached to you for some psychological reason we don't have to speculate about for now. If you no longer are available for him on a dependant psychic level, because you have transcended your addictive tendency, he may just find someone else to take your place, like a girlfriend for instance.
I think you are on the mark with the core feelings. Abandonment in the heart is the core feeling. The anger, fear, and shame are important as well, but we refer to them as first-level feelings. They need to be processed, but the abandonment is the core that is most important. When the abandonment is released, the others will naturally subside as well.
You're doing great work!