So the only thing they didn't really resolve was why Walt left Gray Matter (and Gretchen), right? I guess it's not essential to the overall story, but it's interesting they didn't really explain it.
Walt left Gretchen because of his inferiority complex about rich people/poor people. Something happened at that trip to her family's estate, in something that was said, or the way that they acted that touched his nerve about handouts.
This carries through his character and interaction with her - that he doesn't want their money - don't want any handouts - don't use any of your money to set up the trust fund. This is also why he thinks of "him" versus "the family" because he would have taken their money if he was thinking of the family.