Originally Posted by manimuth
You know, he will always be connected to the mother of his son because of the child. So, accept that because that will not change. And, he is right, to some extent, that you are not part of that relationship between father, mother, and child.
BUT, from what you've written, I think you have to stand up for yourself more. You and your boyfriend must sit down and talk about the rules and regulations of this situation that he will be involved in for the rest of his life. Tell him that he will always have to deal with the mother of his son but it is not right to be involved with her more than the realm of the son they have together. He is only responsible for the care and wellbeing of his son, not her as well. Tell him that he must draw a line when it comes to his son's mother and that it is disrespectful to you to make you feel like an outsider. It is also disrespectful to be secretive with you. There is a difference between being nosy and being aware of what is going on in your boyfriend's life.
So, be honest and tell him how he makes you feel. Explain calmly and work on a compromise. Remember how important communication is, in a relationship. Don't hold onto something that you can end up resenting.
From what you've written, the mother of your boyfriend's son seems to resent you and doesn't mind causing trouble between you and your boyfriend so it is even more important that you keep the communication between you and your boyfriend open and strong.