Help: Should I be his second wife?

I am 28 years old and I request your advice because I am in a serious dilemma. I dated a guy for sometime and I got pregnant and gave birth to a baby girl.

Before we met, there was another woman who claimed to have his son, but he said the child was not his. The woman abandoned the two-month old boy at my boyfriend’s mother. The boy is now six years old and his mother got married a few years ago. She, however, recently separated with her husband because they could not get a child.