I read that just as Hashem was alone before creation so is He alone now.
How can He be alone if He has us, or at least the tzaddikim? [righteous people]
I read that He is all alone!
Your question can be answered by simply adding a comma. He is all alone should be written "He is all, alone."
Hashem is alone because He is all. The Infinite has to be all, or else It would not be Infinite. There can be nothing other than the Infinite.
Yet, even though the Infinite is all, still, there are finite entities, (like you and me) but these do not interfere with the Infinite being unlimited because the Infinite includes the finite.
This is the actual meaning of "One" in the Shema, "Hear O' Israel the L-rd our G-d the L-rd is One." It does not mean "one" in the numerical sense of one, two, three. It means "only".
This lesson is taught openly in the Torah and even though we say it several times a day,[i] since it is so very mystical, few grasp its actual meaning.
The Torah says, "He is the G-d; there is nothing else besides Him."[ii] Why does the Torah need to add "besides Him"? It could have simply said there is nothing else. The Torah is addressing the fact that we do see other things that are obviously not Him, the creation is in fact here. And it comes to tell us that even though there are these other things, still, these other things are not besides Him.
Then, the highest perspective of all does not even suggest there is anything besides Him. "Know this day and take it to your heart that the L-rd is G-d, in the Heavens above and upon the earth below, there is nothing else."[iii] There is nothing else than G-d. He is all, alone.