Spoilers abound, read at your own risk.
  1. He doesn't talk to her. Ever.
  2. He yells at her for getting mad that he doesn't talk to her.
  3. He doesn't tell her he has cancer for months.
  4. He tries to rape her in their kitchen.
  5. He chastises her for not talking to him and then won't talk to her once she asks him a question.
  6. He never asks her about her life (e.g., when she gets her accounting job).
  7. He lies by omission and outright about where he goes (e.g., meditation retreat, visiting his mom).
  8. He does not show up for the birth of his daughter.
  9. He moves back home after she asks to be separated and for him to leave.
  10. He refuses to sign divorce papers for a few episodes worth of time.
  11. He goes back to manufacturing meth after he tells her he is done.
  12. He doesn't help her create and keep their story of gambling addiction straight.
  13. He gets Walt, Jr. a car against Skyler's wishes.
  14. He doesn't return it against Skyler's wishes.
  15. He doesn't go with his family into protective custody to hide from Gus and Mike.
  16. He withholds information about a second phone on at least two separate occasions.
  17. He tells Marie she had an extramarital affair.
  18. He bullies her when she shares her need to save their kids from danger.
  19. He holds a knife up to Skyler and she and Walt, Jr. don't pack bags for escape at his command.
    I don't care if she is the one that pulled it initially, she thought he killed her sister's husband!
  20. But seriously, he never tells her anything. Over 62 episodes, and the only truth we see is his confession at the beginning of S3 and his final words with her in the finale (and even then it's not a full truth of anything).
  21. God damn it, Walt.