Masha, Sasha and Dasha maintained a polyamorous relationship for several months, they formed a loving and sexual trio. And then after a while, the threesome sex became privileged sex between Sasha and Dasha, they got closer to finally realize that they were both in love and that they wanted to have a relationship as a couple exclusive, without Masha. All this really happened gradually, over months, or even several years, I don't remember? The two of them got together before they even left Masha's apartment. Until the last moment, Masha told Sasha that he was the love of her life and that she thought it was a shame to have to part ways like this. If I remember correctly. I find it all the more admirable/balanced that all three of them are still on good terms and friends today, knowing how devastated Masha was by this breakup.