I would argue that the same callous personality evidenced in a person capable of infidelity would also come into play when considering whether or not to reveal said infidelity.
Wouldn't you agree?
Uh, not really. I think you'll find that quite a lot of people are willing to consider engaging in infidelity, but would not be okay with torturing their own offspring on a daily basis in order to keep that fact hidden.
A caring parent wouldn't keep such a thing secret when its causing (continued) suffering for their child. I'm sure there are psychopaths out there where this is not true, but given that they are married, a judgement call is acceptable in my view - even if not ideal.