I'm not sure if it's very wise to make such important decisions based on advice from the internet but I think shezbut laid out the basic options very well. I realize this is a support board and my comments may seem harsh but you are 41 years old. This is your life and your decision and it is a very important one. I agree completely that the welfare of the boyfriend is not important at all. You and the baby are what is important.
How old is your son and have you told him about your situation?