i am sorry that you have to go through this. it is very possible it could be your husbands, but to be 100% sure i would want proof.
you have a right to end the marriage b/c of infidelity if you wanted to.
you can stay with him if you like, but you would have to be very strong for what lies ahead.
i have one child and gotten pregnant on the first try. 1 1/2 weeks after my period i had sex, and my period was due in 2 weeks but didnt come on, and the test was positive.
DNA testing should be sorted out in the begining in this situation. whose name is she planing on putting on the birth certificate. she may not say anything about support, but she has 18 years to change her mind. i was told once you put a person's name on the certificate it's hard to get it removed.
if it is his child what role will he play in this child's life? how will that effect you and if you have any kids? are you strong enough to deal with this if it happens to be your husbands?