Oh Kate... big hugs to you, sweetie. What a mess - but, as with all mistakes, you'll survive. I'm sorry you've found yourself in this position, it's such a tricky one!
I have no personal experience with a situation like this, but I have heard a few times that it's nearly impossible to do DNA tests before the baby is born. There is the possibility of amniocentesis (sp?) or a similar test where cells are taken from the womb and tested, but be aware that these types of tests do tend to carry quite a high risk of miscarriage, so tread warily if you can and want to take that option.
I personally have no strong feelings either way about termination, only the woman involved can decide whether it is best for her or not as far as I'm concerned, so if you do decide that termination is your best option in this instance (and, tbh, if it were me I would probably choose to do so rather than 'dupe' my husband into raising someone else's child, or ruin the lives of the other man and his partner by having it all out in the open, kwim?), you have my support at least. As someone else said, there is a support group for those who are considering or have had a pregnancy terminated, they are a wonderful group of ladies who can share personal experiences and help you come to a decision that works for you.
And again, only you are the best person to know whether or not this should all be aired - I agree with others that a relationship based on lies is not preferable, but then nothing is black and white... you know your situation and you know what kind consequences would come from this, so whether you tell your husband and/or the other man involved is entirely up to you - again, you have my support in that.
I have sadly little knowledge of ovulation and fertilisation periods lol, I've never been 'regular' and conception has happened for me the minute I stop taking the pill so I've never had to do my charts etc, so I'm sorry I can't offer much advice on whether I think the bub you're carrying is more likely to be your husband's or the other man's.
Feel free to PM me if you want to chat about anything, I wish you the best of luck and I hope this situation is resolved with as little pain as possible. Stay strong :)

