I do partly agree with you. Sameer did say he was going along but Rakesh rather irritated commanded him to stay back. I felt it was not right to keep romancing and not go out to his shouts. Granted Rakesh is always shouting unnecessarily but he could be in trouble. Regarding the tea thing, I dont actually blame Naina and Sameer.
Rakesh has never lived with Naina. Since childhood they have lived separately in different apartments so its expected that Naina doesnt know his routine. Before Sameer actually made the effort to get Rakesh to attend Sangeet, Rakesh rarely showed affection towards Naina. In fact it looked like Naina was a burden on him he wanted to get rid off. He was even willing to marry her off to Sharad after knowing that he was an abuser.
He has changed alot now but since they have been kind of estranged their entire lives how would Naina actually know things about Rakesh? But from the upcoming it seems that Naina will make efforts to care for Rakesh and Sameer will do the same.
Yes, Sameer was being irresponsible in not listening to Rakesh's screams. But I agree on your point that Naina has never lived with Rakesh to even know his routine, let alone remembering it.