After reading your story, can see that you truly regret broking off with your ex. You did not mention why you divorce with your ex. But I felt that if the marriage has broke down once and the man has started a fresh start with another woman, no point to linger on...hoping him to return back to your side.
Now, you are burdened with the pregnancy issue which puts you in a very disadvantaged position. To abort or not.....this is really a decision that you need to decide on your own. You should anticipate it coming since you are also a willing party. No matter what is your ulimate decision, i still feel that is good to have a clean break with your ex. We dont't know the cause of your break up with him. But since he has betrayed his current wife's trust by getting initmate with you, he can also stray again. Looking at your deep love for him, can you withstand that stress again?