Even if Tiffany was suffering from post-partum depression, she is still responsible for her actions.
What I can't believe is how easy her husband David is being with her. He wants her back, but has no comprehension of what tough love is all about. I understand the issue of forgiveness, but he needs to demand her respect.
He has all the reason in the world to not accept Tiffany back, and he should tell her to go ahead and start her new life without him and her little girl! That in itself would help Tiffany think about the consequences of her actions. Instead he has given his wife a revolving back door in their relationship to sneak into and out of any time she wants, and there are no consequences. What I hear is: "Honey, I love you and forgive you for running off and having an affair. Will you be coming back soon?" Wow! What kind of respect and trust can you build on that kind of relationship?
Maybe the real issue in this situation is a need for honest communication between David and Tiffany.
I feel bad for their baby. Her mother has abandoned ship and her father doesn't know how to tell his wife to make a full committment or get lost for good. In either case he would be better off than living in a hellish limbo. Were their marriage vows this weak?
If David could develop a backbone, he might be able to save what is left of the marriage. Either way it goes, he has a long road ahead of him. God help him and his poor little daughter. I hope he learns how to stick up for that precious child and gain back his own self respect.