The Chovos HaLevavos in Shaar HaYichud Chapter 7 in the paragraph's that start "The 3rd way" and "The 7th way" explains why it makes sense for there to be only one God and not (none or) two.
1- Can someone please explain to me what he means? How, according to the Chovos HaLevavos, do we know that there are not 2 Gods?
2- Does anyone argue with his thinking and reach the same conclusion in a different way?
(2 other places that might be useful to look at with regards to this topic is 1)Emunos Ve'Deos by R' Saadia Gaon, HaMaamar Harishon Perek 3 the paragraph that starts "Acharei kein hisbonanti" and 2) Moreh Nevuchim, Chelek Aleph, end of chapter 76)