Since you have brought a child into the world, I suggest you work hard at making your marriage work. It doesn’t surprise me that your relationship with your wife isn’t good. She probably senses that you are not committed to her. She is probably both angry and frightened that you will leave her and your daughter. She argues out of her unhappiness.
Stop thinking about the other woman. Let her get on with her life. Get on with yours. Be the best husband you can be, and see how your wife responds. Don’t argue when she is upset with you. Instead, just ask her what you can do to help her be happier. That doesn’t mean you should accept abuse. It does mean that you look beyond the critical comments to her unhappiness and try to respond to that.
Give it time. It will take time and effort on your part to make your marriage a good one. But it is worth making the effort.
All three of you: You, your wife, and especially your little girl deserve to have a peaceful and happy family life. If you can’t make it work, you will be able to separate knowing that you did the honorable thing and tried your best.
I wish you well.