With Al Nassr, Ronaldo can laugh freely with his teammates again, very different from when he was at Manchester United, it seemed like he was very depressed when he was there. There were many internal problems faced, including his problems with the coach. I can understand his feelings right now, because anyone would be surprised when returning to the club while the situation was very different when he left Manchester United to go to Real Madrid at that time.
I also saw that at Al Nassr he was more appreciated and respected compared to his former club which was the club that made his name big. However, I am sure he still respects Manchester United, but for some reason he can no longer have a harmonious relationship. I saw that only Ferguson was very happy and appreciated him when he was at Manchester United.
It makes sense for all three sides equally if you ask me. Ronaldo is a player who has been one of the best ever, not just when he played, but everyone has to agree that he is either the best ever to play this game, or second best player at the very worst case. So him requesting at least a bit of love from the fans, teammates, staff etc is something that is expected and he didn't get that from United but he is getting that respect at Al-Nassr which makes him super happy to be there.
Al-Nassr is showing that respect because they have a player like Ronaldo, 1-2 ever to play the game, so it's normal for them to be super happy, while he may not be in the best two players anymore, he had that and his fame, experience and of course the talent he still has, all bring forward a much better Al-Nassr team, that's an important aspect.
One thing to talk about is United though, he didn't get that much attention because United is not Al Nassr, they didn't need to show him that kind of love, makes no sense for them in the end, they are a big club and they want to eventually be able to win the league again, and showing respect to Ronaldo at 39 wouldn't have made sense to them, so parting ways made more sense.