I know, right? The whole soundtrack is brilliant. I'm not sure if you've heard, but there was actually one song wrote by Ellen McLain herself, which Valve decided not to include in the final game:
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It pretty much confirms the whole "GLaDOS is Chell's mother" situation, as if "Cara Mia Addio" didn't do that already. A newer song appears in Lego Dimensions, about how GLaDOS pretends not to miss Chell but secretly still wishes she was there, but I guess that doesn't count since it's not canon. All the promotion the Portal series has been getting lately makes me wonder if a third game is on the way.