Wow some interesting responses. Not all in line with what I heard here when I first arrived.

First, I am very sorry that you are here and this has happened. Affairs are very painful.
Second, The bottom line for recovering a M applies first and foremost before believing that this woman is pregnant with your WH's child.
Deal with the A first.
Decide what you require for the M to recover, read surviving an A by Dr. Harley. Lay it out for your WH. He feels guilty and shame, and is wallowing in it. He had renewed contact and is confused. So lay it out. My FWH got one chance. Come home, go NC, and work on rebuilding the M. Send a NC letter. Expose to everyone in the family so that they can support you, also his work should be exposed to, or he needs to find a new job.
Third, he is not a father. The time between now and DNA proof that she has had a child that is genetically his is your time to rebuild your M. If at that time the DNA proves that your WH is the biological father, and he wants to father the child, then Dr. Harley does recommend not fighting for the M. You will always be the outsider, and maligned by OW via whatever C exists. If you already had COM then the COM come first and unfortunately the OC needs to not been part of WH's life until the OC is 18 and can interact without the OW present.

Fourth,
Have you been tested for STD's? You need to not have unprotected sex with your WH until both of you have been tested. If he will not go get tested, then you don't have sex. But you must go get yourself tested.

Read Surviving an Affair, read other threads here. Ask more questions. Read in pregnancy for dealing with the possible OC, read over in General for Surviving the Affair.

Fled