My ex girlfriend is keeping me from seeing my 2 year old son. I would like to know how I can get rights to see him. I am not legally the father.

She was married when I met her and living with her husband at the time (I didn''t know this untill much later). She got pregnant had our son in january of 2010. I have had dna tests done to make sure he was mine but she tricked me out of them by saying she was going to change his bc. She has used me seeing him to control the relationship from the start. I have been forced to stay in the relationship even after I found out that she was living with her husband over fear of not being able to see my child. I finally got tired of being controlled and told her it was over. I want to fight for my right to see my son and to support him and be his father but I have no legal rights to do so. I really can''t afford an attorney she is hiding behind the fact that I can''t challenge the father because she lives with her husband. As long as I attach my lips to her backside I can see him every weekend but if not I don''t get to see him at all. Pleas help me what can I do with no money?