Sorry to be a party-pooper, but here goes!
The first time I watched it I was drawn in by the wonderful sceneography throughout, in both interiors and in the stunning episodes by the sea. I could not, however engage with the contrived plot or the generic characterization of the participants. We learn very little about their backgrounds or motivations, and the use of the portrait as a manifestation of the relationship between Héloïse and Marianne is undercut by the problem that the paintings are not very good in the first place. The ups and downs of the affair between the women are predictable and unrevealing.
I watched the film again, with my partner, without saying anything about my views, and she gave up about 20 minutes before the end, saying it
was 'banal and boring'.
Without going into great detail, a summary of my views is that the film is at best a poor relation of Ingmar Bergman's lifelong work - he would take you on an emotional roller-coaster which would disturb and undermine reality for days after.
Two more points: the role of the maid (completely passive and uncomplaining) and the attempts to make her abort, serve little within the main plot and have no bearing on the ending
BUT - the music in the night-time beach party was absolutely stunning!