I might be alone on this but I find the progression of their frinedship over the past 4 seasons to be truly heartwarming.
Starlight went from…
1) Hating Twilight
2) Feeling nervous and unsure around Twilight (Having a strictly Teacher-Student relationship with her.)
3) Becoming a genuine friend of Twilight
4) Becoming BFF's (they pretty much have a sisterly bond with each other, they have fun together while occasionally pissing each other off, like family). They have lived together for so long now that I doubt Twilight would ever willingly want Starlight to leave.
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