Thank you. I have spoken with my Dr about the situation and she had a social worker come in with some counseling options :) My husband is in a delicate place dealing with sobriety and infidelity on his behalf.
I haven't seen a 6 week 5 day ultrasound be any farther off than (at most) a day. I think a date based on a 'cycle' that had a one-day spotting period, is nothing. Sounds like your husband is the father, early ultrasounds are the most accurate.
Does your husband know you had relations with anyone else when you were split up? If not and if you intend to keep it a secret, and if you think the guilt will ride you all pregnancy, see a counselor. I don't think you have anything to worry about, but there are ladies on this site who take counsel of their fears and just can't stop freaking out, and it ruins their whole pregnancy. It can become a problem in the mind more than in the dates (handling guilt). Talk to the counselor, one way to make it better is to determine what you can do to make your husband the happiest daddy in the world, forever.