Ain't no sunshine when she's gone
כְּשֶׁאַתְּ אֵינֵךְ אִיתִּי הַיָּמִים אֲפֹורִים.
The "you" appears twice, in the first and the second word, right? Thus non-formal you could exchange the אינךְ by לא, right?
cshe-at einekh iti ha-yamim aforim
audio for כשאת: https://forvo.com/search/כשאת/
How can you tell that ימים isn't seas?
Plural of Yom יוֹם (day) is Yamim ימים. The two plurals are the same (I think), but from the context, "days" makes more sense as a meaning.
Well, historically they were diffferent (יַמִּים seas verus יָמִים days), but nowadays they sound the same.