Should I quit my job?

Hi. I work in a marketing firm, im dating this guy and I was friends with his crush. Im trying to be friends but its uncomfortable with everyone especially with my manager because she told me not to date him. Apparently she has reason. The crush was like a girlfriend I actually asked him and he denied it. So she was pregnant with his kid, she didnt know because she had another condition he refused to,talk to me about. And she is more sucessful than me, everyone knows and loves her. She left and did some work in another state, and she came back to give birth.
I think she is over him but he visits his son everyday, he was a high risk pregancy , I cant even ask my manager , because she says you decided to date soneone that is interested in someone else. Whats even worse he told me that if I wasnt in the picture he would live with her and make things work. But he says he is happy in a relationship with me but she will always be in a higher postion since that the mother of his child and she is managed by him , so she contributes to his income. I feel im the mistress and she is the golden wife plus she is pretty long hair gorgeous college educated and she doesnt make feel like nothing but I feel that way. What should I do ? Honestly she like her irreplacable moment right now too. Like she dont need him but she really dont. Should I leave him the job or both ?