The ending of Doctor Zhivago - among the darkest in literature

I haven't read the epilogue (set 15 years or so after the "ending" chapter, during World War II, I think) or the final chapter (Zhivago's poems) yet, but the conclusion of the main part o Boris Pasternak's Doctor Zhivago is about as dark and inauspicious as anything I can think of outside of tragic drama (and even in the great tragedies like Lear and Oedipus Rex, there's also the sense of catharsis - some vision of the future even with blood still on the ground or stage). Compared with say the "sad" ending of Great Expectations, the ending of Wuthering Heights, of Crime and Punishment, even Cekhov stories and plays, of Anna Karenina -the deaths at the end of Zhivago are so bleak and meaningless and crushing - once again, as noted in previous posts, it's an inside-out novel, and rather than the deaths being the result of character and action, they're the result of the brutal forces of Soviet society, at least as Pasternak saw and experienced it that destroy the lives of Zhiavago and Lara. But is that fair? Does Zhivago leave his wife, then Lara, then his third common-law wife because of the brutality of the society that will not allow him to express his thoughts and feelings except through underground publications? I think there's a sense that Zhivago is mentally as well as physically ill; his abandonment of the third wife is so odd and unanticipated that it seems the act of a deranged man: he retreats to the solitude of a little room, in the same neighborhood where his wife and child live, to pursue his thinking and writing. We all can appreciate his devotion to his literary vision during a time of oppression, and we can obviously see that through Z. Pasternak is expressing his own deepest needs and fears as a writer in Soviet Russia, but it's also a very heavy-handed way for Pasternak to bring these events to their conclusion - and yet, I admire Pasternak for not succumbing to convention and ending the novel with Z reunited with Lara, forgiven by Tonya, recognized by the world. The ending is not what we expect, but in it's way it's far bolder and grander than what we expect, a relentless vision, an obsession almost, with the evils of Soviet communism, pursued to its inevitable sordid conclusion: two great literary characters who die in poverty and obscurity, alone.