It’s hard to put ourselves as modern readers into the shoes of Pierre and Helene at this point. I would tend to agree with Helene that duelling is a particularly dumb way of dealing with it. But then, what could we recommend: marriage guidance counselling, a quick divorce, “swingers’ parties”, psychotherapy ? None of these are available in 1806.
Psychologically I read this as an internal battle for Pierre: he realises he is to blame for getting manipulated into marriage, and yet he is also tempted to shift the blame onto Helene and her “perversion” - which seems to be mostly invented (“depraved” is the word in my English translation). But, at the time, perhaps any sort of sexual feeling was considered perverse, and more so for women.