This whole thing saddens me greatly. Viewing porn is not infidelity and is definitely not grounds for divorce. Viewing porn can be addicting, and can cause greater trouble within a marriage. I also do no think watching pornography is a good thing to turn to, whether or not masturbation is involved. Can it cause confusion and hurt feelings to the spouse not viewing? Yes, it absolutely can. I am sure that your wife feels inadequate in her new post baby body and feels self conscience about the way you feel about her body now. I don't know her side of the story, but I do know what it is like to be a new mom. I know that if I felt good ole' Unixknight was preferring pornography to me, especially shortly after having a baby, I would feel extremely upset as well. I don't think I would have jumped to "I don't want to be with you anymore" but being hurt and worried about how he felt about me is completely understandable.
Uprooting your entire family, taking your daughter away and going against your vows to love and support each other even when it is hard that you made before Heavenly Father is just not reasonable. Asking for marriage counseling or talking to the Bishop, is.