Sami probably felt like a gut punch was delivered over and over. Everyone kept telling her being with EJ was a mistake, and she went on and on about "he's changed", and the "he's father to 2 of my children" mantras. Especially the "he's changed". So, she put everything else behind her, fresh start, all that malarky. She put her faith in his statements, and was proved wrong, big time. Her ego got deflated, the rug was pulled out from under her, and she fell off of her CLoud 9 with a big thump.
And when she confronted him, he lied again (was just the one time, Samantha), but she knew better. I think that despite all her "putting it all behind her", she is getting back at him for a lot. She had to bide her time, in order to be in a place where it would work, probably ate at her when she wanted to spit in his face. LOL