@SifTheFair idk if tler is native but i'll try to explain it the best i can(and i suck at explaining stuff):
remove the 'red flag' undertones from the word and it returns to its original meaning of 'people who share similar aspirations'
like mangas' 'Nakama'
like xianxia stories' 'Fellow Cultivators'(道友)
and finally, urban city novels' 'Single Dogs'(单身狗)
and this is a case of the latter.
the two of them are siblings that have been established to be 'prime real estate' <- (i use prime because the sister is 'hot'(but not on market) and the brother is 'not'(but he is
virgin territory)
however, family circumstances growing up has forced them to focus more on 'surviving' rather than 'living', leading to a lack of awareness(that is denser than bricks) in regards to their own personal happiness.
in summary: the two of them are mutally jabbing each other about the other party is gonna be 'forever alone'. imo, aside from 'comrade'-同志(Tóngzhì) being a homophone with 'virgin'-童子(Tóngzǐ), the author is also making a social mockery of the old party's emphasis on patriotism where [Country >>> family, food, and sex] is what the siblings used to justify their relationship status.