Where do you go from here? Look for the door marked 'Reality Check'.
You discovered he was having an affair and you rightly threw him out, but you then chose to climb into bed with him and have unprotected sex although you knew he'd been sleeping with an ow.
Were you hoping that a pg would bring him back to you or in some way 'cement' your fragile reconciliation? If so, as anyone here could have told you, you were deluding yourself, honey.
You regard the ow as a 'deeply unpleasant' person because she's texted you, but you sent her a number of insulting texts first so what does that make you?
You wanted 2 dc and you'll have your wish. For the sake of those dc you now need to let go of your rage and get on the with business of salvaging your self-respect and rebuilding your self-esteem.
It will take time to recover from the devastation of discovering that the man you presumably trusted has turned out to be faithless twunt but, as many inspiring women on this board can testify you can, and you will, make a better life for yourself and your dc without him.
How often does he see ds? Is he paying child support? Get these matters in hand and then adopt a policy of having no contact whatsoever with him. This will give you the space you need to get your head together, and it may also concentrate his mind on what he's thrown away and will be missing out on when your new sprog arrives.
But please don't regard this as tactical game-playing. He's gone and you are best advised to see his absence as permanent so that you can begin to structure your life the way you want it to be.
If you haven't done so already, get yourself tested for stis and, if he should come begging for forgiveness, don't be tempted to hit the sack with him again until he produces proof positive that he's clean.
Put the ow out of your mind. She's not the enemy and whatever he's done to you, he'll do to her because he can't keep his flies zipped. Keep your dignity and don't get dragged into any more text or other exchanges with her.
Pain is a given in this life. Suffering is optional. Don't let yourself suffer needlessly just because a deceitful, duplicitous, toe-rag has shown his true colours.