I'm simplifying this a great deal, but that's the basic model. So porn for guys is about sex, and the bog moment is the money shot. Porn for girls is about enduring relationships. Except romances aren't about enduring relationships. As soon as we get to the enduring relationship, the romance is over.
Romance is about everything leading up to the enduring relationship.
Well one of the other things I do when I'm trying not to write is to watch The Learning Channel. And some of the time, the dad probably does know that the kid isn't theirs. But getting pregnant by one guy and getting another guy to raise the child doesn't fit in with the evolutionary model. And more and more animal studies are showing that females often cheat because there may be an evolutionary advantage to having a bunch of, well, call them lovers because 'back-door man' is a little to anthrocentric, is that the lovers are invested in the offspring, too. Because they never know if it isn't their offspring.