Inversely, I don't recall if there's a point where the game forces the MC to cum inside Nicole, thus someone might have a playthrough where it was impossible to knock her up.
I believe majority of the sex scene that MC (Us) has with Nicole you have two options, "Cum inside Nicole or Don't cum inside her." But I believe majority of us chose to force to cum inside Nicole.
There have been sex scenes where Nicole wants MC to cum inside her. In Day 9 after their first date, Nicole wanted MC to cum inside her. After that they have multiple sex sessions or rounds in different positions and I'm assuming in each of those rounds MC has cum inside her. The Night time LBP beach (I believe you can only get this scene if your Nicole corrruption points are high), Library sex scene in Part 10, are other sex scenes in which Nicole wanted MC to cum inside her.
They're other sex scenes where if you did cum inside Nicole she didn't mind and judging by her body language, ogasm and facial expression she wanted MC to cum inside her, whether you have the option to cum inside or don't cum inside Nicole. Does sex scenes are, the School Dance, Bikini Try, the hotel sex scene at LBP, Massage shower at LBP, the bathroom sex scene in Part 9 and the first sex scene we have with Nicole in Part 11 (if you're on the love path with her).
provide John grounds to convince Nicole to keep the baby rather than aborting it out of fear her husband would discover the affair via a pregnancy he did not consumate.
If the game is heading towards for a pregnant Nicole and to have MC's baby. I don't think it will take a lot of ground to convince Nicole to keep the baby. Or which I believe she will instantly decide to keep MC's baby. This is how I imagine it will play out.
Once Nicole discovers that she is pregnant with MC's baby she will first have her doubts but she will definitely and immediately decide to keep and carry MC's child. How do I know this? Throughout the game it has been showing us already that Nicole is a loving mother and would do anything for her child. If we're on the route towards Nicole saying the words, "I love you" to MC (Us). These two evidence are the reason why she will keep MC's baby.
Also the name of the game can be mention again if Nicole reveals that she is pregnant to MC and also telling him that she will keep his child. MC will ask why or what changed her mind but Nicole may reply with, "this is what A Mother's Love is." and she will end it with the phrase, "And because.... I love you."
On the other hand, the fact that you mention Viagra has given me the idea of being able to explain the change of sheets mentioned in the blurred screenshot: Nicole, for whatever reason (whether due to a timely call from the missing Silvia or due to a categorical refusal from Nicole, citing not feeling like it right now or the danger of being overheard by Chloe), refuses to have sex with her husband, and he is forced to relieve himself, staining their bed in such a way that it needs that change of sheets.
I love this theory and this would explain the change of bed sheets.
I suppose it could be both, that he enjoys taking women away from other men, but has to use Viagra as a means to do so, but anyways I guess we will have to wait and see.
It is a possibility that these two theories can happen. John may only be attracted to women who are in relationships or in deeply in love with another partner but he may need Viagra to help keep his manhood up.