Hi OP,
I'm sad for you that you are in this place. There is something you can do about it, though. Fortunately men are much more successful at pursuing their marriage when they want a change than women are.
So first of all, the woman you have grown an attraction to is providing a contrast effect to your wife. As long as you have contact with this woman, your wife will never be attractive to you. If you want to raise your child with a wife you love, you must stop seeing this woman. If you work in the same building or will see her at work, you literally need to change jobs.
Second of all, it is a statistical fact that people affair down. Think about it: what type of person is OK with having an affair with a man who has a pregnant wife, and breaking up a family? This person is not in the cream of the crop. Selfishness is the impetus for an affair, and you will receive it in spades if you forsake your marriage for this other woman. This is not just a pious lecture but it is borne out by studies of 1,000s of marriages who have suffered affairs. Affairages (marriages to affair partners) do not survive the rigors of a marital situation. Sooo.... as attracted as you might be to this woman right now, know that your future with her would be an ugly prospect.
Third, imagine how your life would change when your affair is exposed to everyone you know. It's tantalizing to place yourself in the fantasy, but now imagine explaining how you broke up your child's home in order to get between the sheets with another woman to your parents, siblings, her parents, your church, your workplace. That will usually break the affair anyway. So now you hurt everyone you know for what?
Finally, you can have wonderful and romantic marriage with your wife regardless of how you feel today. As the husband, you can successfully pursue her back into a relationship of extraordinary care for each other. The way to do it is to avoid doing things that hurt each other, do things that build up love bank deposits and date (like you did when you fell in love). If dating is how you feel in love, how do you expect to stay in love if you stop dating?
Here is a link to a marriage building methodology that has been fantastically successful whenever it is followed. Dr. Harley studied 10,000s of marriages and flushed out a formula for how happy marriages stay happy. He is now in his 70s and has used this methodology his whole counseling career to fantastic success:
Dr. Harley's Basic Concepts
Please take a look around at that site. If you have more specific questions, you can post them in the guidance forum there and trained volunteers (supervised by Dr. Harley) will help you.
May God bless your decision to reach out for help. I pray that you are able to arrest this train wreck before it happens. Once you stop thinking after the other woman you wife will become more attractive to you.
Blessings,
E.