NEW SERIES: Spiritual questions that people ask in therapy: Am I selfish if I say no?

Today's questions: My mother has a very giving nature, she never kept anything for herself, if she just brought herself a new outfit and someone said to her that they liked it she would say, "here have it!" The flip side of that is that she expects everyone else to be the same way, if I was playing with a toy and another child came over and wanted to play with it then she expected me to give it up… if I didn’t I was called selfish, and told I had bad middos… now as an adult I am trying to learn about how to have healthy boundaries, and I find that I have a lot of confusion and internal chaos, around this area, when I say no I have a voice in my head that is saying you are selfish and you have bad middos and when I say yes I feel resentful and then I have another voice in my head that says see how crazy you are you can never be happy for anyone… and then I feel guilt and like a horrible person… so my question is, could it be true that I just have bad middos? Am I selfish if I say no?