I'm busy today. Sasha is not here too
(Sentences are not really related)
http://www.grammar-quizzes.com/too-either.html says "either" should be used, but wanted confirmation.
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"I'm busy today. Sasha is not here, too."
If the meaning of the "too" is "This is something I'm telling you in addition to saying I'm busy", then "too" is okay. But if the meaning is "I can't help you, and Sasha is also not available to help you," the "too" should be replaced by "either".
See Georgia Green, 1968, "On too and either, and not just on too and either, either." pp. 22-39, in Papers from the fourth regional meeting of the Chicago Linguistic Society.
As far as I know in negative sentences we use either or neither instead of too so the correct form of the above sentence is: I'm busy today.Sasha is not here either