If you divorce with shared guardianship of a grandchild can you be legally sued for child support?

I divorced my ex while we shared guardianship of my grandson. She kept the grandson. We have been divorced for 9 years and the divorce decree does not address this issue. The child is now 12 years old and living with his biological mother but I have never dissolved the guardianship due to a dread of the aftermath of such a move on my part. My fear of my ex coming after me for child support is keeping me in a position of tolerating non-stop drama and invasion of my life by my ex. She has remarried but will not leave me alone. She keeps something stirred up and I cannot develop a good relationship with my grandson because of her. I divorced her because I wanted to escape from her behavior. I don’t have enough financial resources to seek legal counsel. Has anyone ever dealt with or know of anyone with a similar story and if so can you share?