Honestly, I think that Joesph had that same questions when he found out that Mary was pregnant and he had never been with her.
I think you can raise this child.
I can understand your fears, but the thing is that this child didn't ask to be created. It was created by our Lord.
You love your wife. This baby is part of your wife.
Let me tell you something. In the 1970's my white mom was raped by a black man. She got pregnant. Her husband at the time left her, even after she had an abortion. I'm her child from her second marriage. I still wonder if that little baby would be an older brother or sister to me. I really don't care if my "older" brother or sister would have been all white or all black. I just wish I would have met him/her because they would have been a part of my mom and my family.
Making things more broken because you are broken up isn't the way to go in this situation.
In the end, it's time to do what Jesus would do, even though it's hard and scary. Jesus wouldn't run out and get a divorce at the first sign of trouble. Jesus wouldn't encourage your wife to have an abortion because it's convenient and people want to forget their emotional trauma. An abortion will only add to the emotional trauma, not lessen it.
You'll tell the child the truth when it's time and let the child know that despite your fears, you choose to be his or her dad anyway because that's what the child needed and that's what a real husband does. He doesn't leave his wife, even if she makes a horrible one-time mistake. (It was a one time thing, right? There isn't a pattern, is there?)
Of course, the child will have questions about bio-dad, that's human.
I can't imagine how heartbreaking all of this is for you, but I think you need to talk to a priest. (I know, don't all CAF threads eventually say, 'talk to your priest'? But it's true. Priests are there to help us through times of crises.)
Good luck to you.