Pregnant at 16 is not the same as pregnant at 27. If you don't marry this creep (yes he's a creep), will you be able to find a husband when you are 35 and trying to date again? The more kids you have and the longer you wait, the harder it will be to date and find a real husband for the family you want. A lot of guys don't mind a 10 year old kid when dating, but another newborn will not be conducive to seeking a lifetime partner. Don't make the same mistake twice. Did I say your 10 year old daughter is a mistake? NO. Your 10 year old daughter needs stability, not a lying manipulative creep step-father who doesn't seem to care about you or makes you come second after his first family. Do you really want this creep to be the new father to your 10 year old daughter?
My gut tells me this creep is bad news and that he is not the husband you want. My gut also tells me that you have a pattern of falling into these situations, letting things happen to you instead of planning things for your future. Take care of your daughter, yourself and your future by finding a quality husband first, THEN if you BOTH decide to have a baby that you can both commit to, do so.
Not to mention the financial and time demands if you have a child now. A real husband would raise a baby with you. I doubt this creep has any intention or even ability of helping you raise his/your child other than child support payments. Don't you deserve better?
Don't just think about the baby, think about the family, husband and future kids you might be giving up if you do not get an abortion.