Behaviour problems

My 7 year old has been talking back a lot lately and getting worked up very quickly. We have a new born at home but we manage to give each of our 3 children the attention they are mostly used to. As much as possible. But I don’t believe the problem lies here.

He has been spending a lot of time with his neighbor friend who is 2 years older and i feel like that’s changed his attitude quite a bit. And I’m not sure what I can do to get my fun loving 7 year old back