This is what people get wrong about relationships and who Nukumizu will end up with
For a moment, let's just forget about all the dates, the chemistry and the cute moments and think seriously about what a relationship needs to sustain, because those are just the honeymoon period, most couples will need to learn other ways to stay together past it.
Then what can we rely on to keep our relationships going strong despite the hardship that life may throw our way? Probably the only answer to that is Trust. You've just got to trust your partner to pull through whether they may meet somebody else or simply spend more time with other people than you. In the face of relationship adversity, trust and sincerity are probably the best weapon anyone can wield, because a good partner will actually try and meet your expectations.
In the story, we (in Nukumizu's POV) actually see how other relationships play out, where they succeed and where they fail, what it takes to work. It'll be shallow of us if we assume Nuku doesn't learn from any of this. For the sake of a good story, the author will likely pick the girl that Nuku thinks is right for him after going through all his experience, rather than the girl that the audience thinks is right for him.
And tbh, I don't think Nuku has shared a more trustful relationship with any girl other than Komari so far.