You might be surprised by my stance on this topic, but I absolutely think romantic relationships are somewhat collective. Haven't you ever asked your girlfriends for advice on how to respond to a text message?
I'll go further and say that if your relationships aren't at least a little bit collective, you should work on them. I'm not saying you should expose every part of your intimate life or your partner's. I'm saying that by sharing different points of view with different people, we enrich our perspective on the issues that stem from our relationships.
We might think we are right about a subject while arguing with our loved ones, but as soon as we discuss it with someone else, in a space where the stakes are lower, we realize we weren't as right as we thought. I think that's the main way in which humans have shared knowledge and stayed flexible and civil throughout history, so I will always stand by any form of 'healthy gossip'.
Of course, I understand the man in this story took it a step further and completely removed himself from every discussion while he waited to receive orders from someone else.
The question is, is the girlfriend then ready to have a relationship with him without his sister's assistance? Will it be much different? There is a chance she might not even like him after all; I mean, she has yet to know him, because she has been practically dating his sister up until now!
What would you do? Would you give him an opportunity and prioritize everything else they've had during the relationship? Or would you consider this a deal-breaker and not an innocent need for reassurance?