"what does a man do; look after his family despite everything" this quote from gus pretty much sums up walter's purpose. he used the criminal opportunity not for the family but himself. I also don't think this is completely about his selfishness.
he wanted a personal salvation to get out of what happened in the past by vengeance as it was the only thing he had from what he experienced in his criminal record. imagine once again an extremely overqualified high school chemistry teacher dealing with bunch of spoiled kids, even get humiliated by them. he would be disciplined by an ignorant car wash owner that didn't even have quarter of his vision. all these could be chain reaction starting from unfortunate events of gray matters company. maybe the marriage with skyler could be his attempt to move on and put things in the past.
she did what walter did, and she is as much guilty as walter is. but I see nobody is calling walter a bitch(except jesse). clearly skyler's actions weren't as sophisticated as walter's. I could only think summarizing the whole plot with "ooga booga bitch woman" is just cheap approach to complex storyline. they both betrayed in their family but skyler's betrayal was highlighted as she made such popular sin.