I can't stand stories where the h is pregnant with the H's baby but tricks the OM into thinking the kid is his. It makes you wonder how many times that game was played before DNA tests? Way too many, I'll bet.
While it's true the OM was a jerk, it still doesn't excuse the h trying to pass the H's baby off as his. And if the H had been more truthful in the first place, and the h had trusted him more, the whole deception wouldn't have been necessary.