I know you are hurt. I get that. I have felt that.
It is a hard thing to hear that your wife has been with someone else. Hard to get your mind around it.
As I have had no experience personally with porn addiction, I can only imagine how it made her feel.
But I am not here to judge, nor to tell you how to feel.
You are angry and hurt and your thoughts are understandably all over the place.
Once you have some time to think through things, I believe you may see things differently.
You are allowing your anger to take over what your heart is feeling...disappointment, sadness, and maybe even feeling foolish that you didnt see it.
The truth is that marriages survive affairs and porn addiction. But you can only take care of your side of the street. You have no idea whether she is capable of working through stuff. Thats not really your place to decide.
What you do need to decide is what is best for you. You need to do that from a place of strength, not anger. Do it from a place of compassion for the mother of your child and the woman you love. Do it without judgement of her because all of us contributed to the problems in our marriage.
Take some time. Regroup.
Be careful to own your stuff and only yours. She has to own hers.
If, after you decide within those parameters, that you can no longer stand, I will support you completely.