What, this woman has been trying for 7 and a half years to fall pregnant, and she decides to quickly to fly down, and agrees to unprotected sex knowing full well that she was highly fertile, 4 times, and shock horror, she is pregnant and left her husband for yours...? Bullshit.
She knew what she was doing. I would bet on her being so desperate for a baby, that she did this and then her husband found out and then left her. In what reality does someone shag a bloke who you barely know, unprotected, when they are at their most fertile?
They deserve each other. Neither will trust each other, knowing how they both can't stay faithful and they are just as sleazy and deceitful as each other. Leave the dirty weasels to each other!!
You, my dear, are worth FAR more than the pair of them together. You will one day find someone who will be the complete opposite to the shit for brains bastard, and will be happier than you ever was with him.
Good luck, and take all the above advice. He is going to make it difficult for you, I bet!!