"Far from Home" didn't make a lot of sense. I didn't buy that plot at all. Supergirl only knew Brainiac 5 for 12 hours and just like that she abandons her old life, her family and friends so she can shack up with him in the 31st century? She barely knew him. What if it doesn't work out between them? Kara would feel pretty darn stupid if she and Brainy broke up a week later.
I'm sorry, but I just think that the writers should have been able to come up with a better reason for Supergirl to leave the League forever besides a mere schoolgirl crush. That was pretty weak, IMHO.