Student or Learner
Please, would you tell me if this sentence is grammatically correct:
He has been watching all these years his friend making money by selling his paintings to the rich, and he has decided to become a painter himself.
I don't disagree, but would suggest moving "all these years" to after "to the rich" as a more natural word order, even more so than setting it off with commas.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.