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"Ты - супер!" sounds a bit like a teenage slang ("You rocks!").

Ты - лучший! - You're the best!
But I prefer "Ты лучше всех!" instead, which is almost the same ("You're the best of all"...

Yes, I think these are the best.
Good luck! :wink:

Sounds weird a bit, "разлучиться" is mostly passive ("их разлучили во младенчестве").
Here it also implies (imho) that now they are "together" (like a pair).

How about "мне будет очень грустно, когда/если мы перестанем с тобой видеться"?
I don't like finality in the "больше не увижу".