Nah b, it wasn't that simple. Gretchen was his ex and from what we know things ended badly between them. He harbors some animosity for them because apparently all their success is owed to his contribution to that science thing (forgot what it was called - grey matter?). They became super rich and even got a nobel prize due to WALT'S work (at least from what we know), and he ended up being an over-qualified high school chemistry teacher. You can't fault him for not wanting to accept their charity.
I wouldn't blame the deaths of the plane crash on Walt either. If you are gonna go by that logic, it is technically Jesse's fault for allowing her to relapse and going down that path again, etc etc. Him being more concerned about his marriage in the end and seemingly oblivious about the crash when it happened spoke more of his character and his mind state at the time, but I wouldn't put the responsibility all on him.
didn't he turn her on back though?