Oh! I get it now. Personally, I don't think it's something bad so far there is a mutual understanding between them and one is not trying to hijack the friendship. Mutual understanding is very important in such friendship...
That's exactly where I'm driving at. For me as well,I don't think it's bad
Friendship is not an enclosed one not open to extension because of the fear of losing our touch the other. There was something lacking in the friendship in the first place and not because of the third
Now you get my point... nothing bad in extension.. understand eachother is thesin key