Mari is in contention to play on Wednesday when Arsenal head to City.
The defender previously spent three seasons at the Etihad before joining Flamengo, but he never played for City as he was loaned out repeatedly.
“In that time, for me in my mind, I wanted to play with them. This was not possible," said Mari.
“So now for me it is another situation. I want to play a lot of years here with Arsenal. It is another situation and I am really happy now.
“It is going to be a nice game [on Wednesday], but I am really focused here now with Arsenal. I want to win that game. It is one more game for us, another three points and we want to try to win.
“I've learned a lot because when I was there [at Man City] I was young, now I am little bit older.
“I learned a lot in all the teams I have played. So I think it is different. I am don't want to look back, I want to look forward.
“Now I am in a really good club and I want to continue here for a lot of years."