He couldn't come back, even to visit his mother?

Going from the TC, it implies he becomes absorbed into his high-flying lifestyle as a big-shot. We see him so moved in the ending because he connects to a time that was simpler but definitely more real. I guess its one of the reasons why he has so much trouble holding down a long-term relationship, the fame and fortune made him forget his true self.

But yeah, he kept in contact and who's to say that he didn't invite his mother to visit, after all he did continue to support her financially. Also Italians especially in the South are very connected to their roots and family so maybe she chose to stay?

He never came back first because Alfredo ask him to never come back. Second becasue when you are an immigrant even from one city to another you have to leave everything behind is the only way to succeed if you are thinking of coming back or you have a plan b you are dead. Third going back was to painful for him, he was and always will be in love with Elena.