If I were you, unless the man is willing to file a divorce with his wife n decides to marry me, if not I would not keep his baby. It is a life time commitment n it is unfair for the baby to grow up in such a situation, fatherless. It will be a humiliation to the baby as well when he or she grows up.
Although it is a life, but if you choose to keep his baby, then you will have to bear all responsibilities, I think it is not easy to bring up 2 children at the same time. I have seen lots of cases, I dont't think the man will bear the responsibilities coz if he chooses to file for divorce with his wife, he will need to pay maintenance fees.
Most men will not choose to do that. Eventually you are the one to suffer. It is also totally a big mistake for him to commit adultery!!
Since he could do that to his wife , Im not surprise he can do that to other women if he ever marries you.
I personally do not feel that he is a sincere man at all. Sorry to comment on that.