Kimmy,
By keeping this boundary clear you are reaffirming your right to stay strong and keep undue hassle out of your life. The mother and her issues are just that
her issues! I am sorry if she is so petty to allow her relationship with her gs pass by due to her own selfish issues.
You are not selfish! Selfish people do not do things for their best intersts. They just do things because they don't ever want to bend to another. You are someone who knows what compromise means and how to do it. This
is not a situation to compromise in!
You and little man have a wonderful relationship. His being hurt by not have gm time may seem sad in this moment but in the larger picture it is better for you to establish and keep this safe boundary with the mother than to make sure the mother gets her way with little man while continuing to treat you poorly. Bleh! No thanks!
You are so strong to be doing this KD. I believe in you and the little man!!