Are you in a country or a culture where you cannot get a divorce?
My advice will change if that's the case (and I suspect it is).
But just in case it isn't, do NOT bring a child into this marriage. It won't make anything better; it'll just add work for you. And I don't mean you won't love your child or hopefully receive love in return. What I mean is, in a cost-benefit analysis, you would likely be taking on most of the responsibilities and are already stepping out on your marriage.
When your husband figures out you cheated on him (not if, but when), it will not be pretty. Don't drag a child into that kind of mess.