I can understand failed IVF driving a couple apart, but I would have thought a pregnancy and baby would unite you. Even if the relationship has issues you're bonded by the experience, because you rely on your partner a lot during IVF and its a team effort.
Having said that, of course sometimes kids show up cracks in a marriage. So you separate or divorce. However, I'll admit that the first year of a baby's life we were so busy working out how to be parents and having no sleep I don't think we would have time to work on our relationship, much less divorce.
But shagging the boss and leaving when your kid's not yet 1 - well, that's an interesting choice