I am sorry to hear about your marital issues, and your struggles.
I am not a lawyer, but I think you need one. I say this because it MAY be possible to have your name on the birth certificate as father and that will end the issue. But you and your wife must be in agreement, and the putative father has no right to either demand an abortion or that the mother keep the baby. that is simply not his choice, but because he is seeking an abortion of the baby, that may alleviate the issue of paternal support he would need to pay if the baby were to be delivered.
As to the reasons for unfaithfulness, I believe that you need to look in the mirror. Women as a general rule do not cheat unless they believe that the marriage is beyond repair, so in this counseling, you need to SACRIFICE yourself in order to woo her back. Look at Paul's instructions to husbands in Ephesians 5, and determine where YOU failed. If you lead her properly, she will follow, and willing do her part.
This may be hard to take, but considering the consequences of denial and blaming the other will cause long term chaos if both of you do not seek to put Good first, and seek to have Jesus glorified in the outworking of the situation.