I'm sorry this is happening. This is a tough call that only you can make. Just to be clear: You owe her nothing. She and the father are responsible for the child, NOT YOU.
First, you have to decide if you can trust her enough to be in a healthy relationship. Take your time to think about this. If your answer is no, there's no point in thinking about the baby.
If the answer is yes, she and the baby are a packaged deal. Raising a child is a life-changing, life-long decision. Don't just think about if you're willing to commit to a child today... are you willing to still be committed when it's a monstrous 2-year-old, or a teenager that you wish you could strangle? Do you want to run to soccer practice? Do you want to stay up all night working on a life-size Frankenstein for a project that the kid didn't tell you about until the day before (that's what I was doing Sunday night!)? Do you want to divert your earnings that could be going toward fun, vacations, or retirement into the kid's college funds. Kids are no joke. Do you even want to be a mother, or is your attachment to your ex clouding your decision. If you don't want to be a mother, there's no point in thinking about any of this.
But really, if you don't think you can feel respected in a relationship with your cheating ex, just walk away. You'd be well within your rights to do so.