There is a foundational discussion of friendship in Aristotle's Nicomachean Ethics.In Symposium Plato presents the nature of love through the speeches of his interlocutors, especially Aristophanes'
speech on one's 'seeking one's other half' and Diotima's speech at the end about Porus and Penia.
Love is not just eros, but agape, philos and storge as well — see C. S Lewis' The Four Lovesfor an
overview and Pavel Florovsky, The Pillar and Ground of Truthfor a philosophical account.
Does God exist? Not like a existent among existents. The traditional theological account definitive for
orthodox thinking on this question is in The Divine Namesby Pseudo-Dionysius (in print in the
Classics of Western Spirituality series by Paulist Press). One of the most famous accounts of this
question is that of Thomas Aquinas; see the Oxford World Classics edition of Aquinas's Selected
Philosophical Writings,passage 20. Anselm's so-called ontological argument for the existence of
God, to be found in his Proslogionhas been criticised by all major philosophers from Descartes
onward. All these critiques of Anselm can be found in the Introduction to the Open Court Classics
edition of Anselm's Basic Writings.