You asked what “splitting the mind in two” means. Let me give you the rest of the quote. You should reflect on the Greek Myth, Pandora.
“It was Sappho who first called eros "bittersweet." No one who has been in love disputes her. What does the word mean?
Eros seemed to Sappho at once an experience of pleasure and pain. Here is contradiction and perhaps paradox.
To perceive this eros can split the mind in two. Why? The components of the contradiction may seem, at first glance, obvious. We take for granted, as did Sappho, the sweetness of erotic desire; its pleasurability smiles out at us. But the bitterness is less obvious. There might be several reasons why what is sweet should also be bitter. There may be various relations between the two savors. Poets have sorted the matter out in different ways. Sappho's own formulation is a good place to begin tracing the possibilities. The relevant fragment runs:
"Epos snûté Hi' d luoLichns Sóvel, yuKOnikpov auáxavov optErov
Eros once again limb-loosener whirls me sweetbitter, impossible to fight off, creature stealing up”
(LP, fr. 130)
And this — also in the book:
“To love one's friends and hate one's enemies" is a standard archaic prescription for moral response. Love and hate construct between them the machinery of human contact. Does it make sense to locate both poles of this affect within the single emotional event of eros? Presumably, yes, if friend and enemy converge in the being who is its occasion. The convergence creates a paradox, but…”
This is a difficult concept dave.