I don't get the impression Ruby likes Blakeney in a romantic sense, I simply think it's a very intense, bordering on toxic friendship that will eventually just fizzle once they no longer live together.
We've had no indication that Ruby had many friends prior to Blakeney; I cannot remember in her early school vlogs detailing any friendships, other than ones that were introduced by the family and forced upon her. As Ruby feels she has lots in common with Blakeney and has finally found a great friend, she tries to hammer this home by extreme adoration, whether that be Instagram posts, buying her things, sending her constant letters. The whole "best friend" thing does appear somewhat childish, but don't things there's necessarily anything wrong with it, but the issue is we have no idea how Blakeney feels. She never asked to be on social media and now has people recognising her face and knowing details about her life, when I'm sure that was never her intention; if it was, she would have started her own platform.
From experience, this level of intensity will never end well, especially when one person seems way more invested than the other (not saying this is true, but it's a fair assumption). It's difficult to avoid this when you live together, but when they're apart, I'm sure Blakeney will get her own life and work, find a partner and enjoy her social life, whereas Ruby will continue to drift on her gap year and wonder why Blakeney isn't returning her calls and letters.
It would have been very beneficial for Ruby to find a wider circle of friends rather than relying on one, crazily intense "best friend" situation, but suppose it's a bit late for that now.