The rules of Baby Mama Etiquette?

I recently started seeing a guy I work with. He had a baby boy 2 months ago with a girl who also works with us. He has no feelings for her, but she recently confronted me and admitted (in tears) that she is still in love with him and that it was wrong of me to get involved with him because they have a child and we work together and she and I are friends. She has been asked on numerous occasions about her feelings for him and she has scoffed him off and denied anything.

She lied to him about birth control use in order to get pregnant by him and then made excuses as to why she had to go through with the pregnancy. Basically, she is obsessed with him and wanted to have his kid so she would always be tied to him. She claims that I have disrespected her and then in turn disrespects me. I have talked with the baby's father about it and he says that he will not listen to me talk negatively about her because she is the father of his child. He wants me to act like there is no situation, but I feel like she will always have it out for me because I've "stolen" her man.

I was told by a friend that I broke baby mama etiquette by being with him because she and i know each other and work together. Is this true? And if so, what should I do? I really care about him.