Sweet mari, I wish that all this pain you are going through will end soon. I'm sorry I didn't post here earlier to give you any suggestions or anything (for the longest time I thought I did...).
But to be completely honest, all I can tell you for certain about your life is that one day, like everyone in this world, you will die, and your son will always remain your son. Why am I saying this? Well, I personally think that if you are running a risk with the possibilities in this relationship, it may not be the best choice for your son. I'm not sure how much a father figure helps in a child's life, I've always accepted the fact that I have both parents, but during those guy moments later in life (birds and the bees, first dates, how to shave, etc) I know I relied on my dad a lot.
I don't know what happened to this woman, but apparently she now thinks that she has the upper hand since she was with your master first. If your master does not come to a decision about the whole relationship, I think that you should confront him with not only yourself, but your son in mind about what choices he plans to make.
Ofcourse, it is simply easy for me to say all of this, I know it must be infinitly harder in your position to follow my advice. I also don't know everything about your life, and just made a few assumptions on what you have written in this thread, so if I said anything that may be or is offensive, I'm sorry. Whatever you decide to do in the end, I hope the best of luck for you, and that whatever happens, you will be happy in the end.