I am so sorry OP you are going through an awful situation when you are heavily pregnant with a young child .
If you haven't already packed your hospital bag with maternity notes have them ready .
I am not sure if others have mentioned but the Surviving Infidelity website is a good source of info . It is American , so not all of it is applicable here .
You have to make sure you eat little and often and keep hydrated .I know you will be struggling to sleep
but try and have some naps . I found the radio3 wind - down app useful for this and not a classical music fan .
I am so sorry that you have also encountered very little back from your H . He should be absolutely disgusted with his own behaviour .
It does seem that he was not aware that the OW was going to spill the beans . You have to accept that neither of them had you and your family's best interests at heart . If she had just found out that you were pregnant again and had been fed lies by him , surely she would have kept quiet rather than divulge to you so close to your birth .
Your husband has been able to compartmentalise his feelings and has been devious and deceptive throughout . Also look up cognitive dissonance , he will try and make out that you were at fault / to blame for his actions .
Anyone who can cheat on a pregnant wife with a young child already , is surely the lowest of the low . He will be concerned about his reputation as impossible to gloss over this situation .
You will be on a roller coaster of emotions going forward and will think of happy times with him . Unfortunately this has now been tainted with what you now know .
You cannot trust anything that he says or does now . He is looking after himself .
It seems like you have a great support network . Do not ever feel guilty that you should have known / somehow caused this . I think most people know that partners can cheat , but when our lives are enmeshed with a partner , we have set up home and have a family we do think we are a tight knit unit and that it won't happen to us . Sadly we are both aware, it can .
Look after yourself and just take it day by day .