The only scene in the entire movie I didn't particularly care for was the argument they get in to, if only because it felt like they were trying to force some tension into the relationship when it was entirely unnecessary and didn't really have much payoff.
With the argument I just felt like I was having a stereotype guy moment because I couldn't even figure out what they were arguing about, even the second time through.
i know this is more about what they're arguing about rather than how it happens but damn when you're having a good moment and the mood just suddenly shifts because of one thing a person says, that felt too real
As for the scene and argument itself, i think there's some interesting stuff there as Marianne is forced to confront the inevitable end of their relationship. It starts with them talking about how they've changed since they first met and because of how their relationship has progressed, Marianne now resents Heloise ("you bear me a grudge") because Heloise is not stopping the marriage. Marianne is placing that "burden" despite knowing deep down that neither of them really have that power. I think it's also interesting that Marianne says before that by painting and finishing the portrait, she "give[s] you (Heloise) to another" so she is crediting herself with some action here (although it is subs). Heloise is hurt because she feels misunderstood by the person who she thought knew her the most when she had been resisting up to that point and in the end "gave in" to the marriage because by allowing to have herself be painted, they could have that time together. But then she's basically getting called a coward by someone who's not even definitively asking her to refuse the marriage and also giving in to the same societal convention ("You'd prefer me to resist." "Yes." "Are you asking me to?" "No.")