Notre Coeur is one of Maupassant's lesser known novels - of the six he wrote, three are perpetually in print in English, and three are hard to find. I got this one (as a present) via abebooks, in a 1946 edition.
It's a simple love story - André Mariolle becomes obsessed with a widow, Madame de Burne, a hostess of some beauty who cultivates exclusively male friends of some talent for drawing room soirées, each of whom becomes slightly obsessed with her, encouraged by her flirtation, but never succeeds. Mariolle does, with an assault of attention in person and by letter, and they start an affair.
Their input into the relationship is uneven, however - he is jealous and demanding, and despairing of her seeming casual attitude to him; she is flattered by his attention, and enjoys the physical relationship (delicately alluded to), but cannot love him in the same way, as he demands. Maupassant describes their developing emotions in typical analytical detail, with great sympathy, immersing the reader in the relationship and alternating between the protagonists. He shows an understanding of both sides of an obsession, and of how relationships with unequal passions arise and play out, probably described from experience.
The novel suffers from being just about the one affair - it's quite short, and in a narrow world, although this is typical of his stories and novels. It ends with a nice irony - on the rebound from Mme de Burne, André starts an affair with a maid who he hires, and treats her in the same way that he has been treated, receiving her adoration, having encouraged it, but not reciprocating it. The novel has a satisfactory circularity, and explains the title, 'Our Heart' - love is like this for all of us.