Michelle - he's Behaving like this because he's a selfish bastard . It's not because you are " not enough " is any way .
And as others have said, YOU didn't have an affair because you didn't know he was still married . It's not your fault .
You both used contraception, but it's not 100% reliable . That's not your fault .
Please stop blaming yourself for the situation you are in . Blame won't help you now , you need to look at the options open to you and work out the pros and cons . You don't need to do any of this to HIS timescale , although of course there is a time limit on your termination options.
If you decide to keep the baby, don't think that you need to tell everyone about the baby's father being married . You don't. You just say that the father isn't around anymore - you had a short relationship and it didn't work out .
Yes he has to pay child support . I think he would be very keen to do this without any fuss, if he wants to stop his wife finding out .
It's sad that he wouldnt to see his child, but lots of kids are in this situation and they cope ok. After all , your child will have loving siblings and mum.
Can I just say that you do have another option, which is to have the baby but place them for adoption ? It's not an easy route , but it's right for some women and their families . However , the baby's father would be interviewed to see if he or anyone in his family wanted to bring up the child , and that might not be acceptable to you.