The python
How impossible it was for me to live without seeing her! And with each of my
actions, even the most trivial, since they had all been steeped beforehand
in the blissful atmosphere which was Albertine's presence, I was obliged time
after time, at renewed cost, with the same pain, to relive the first
experience of separation. Then the competition of other forms of life thrust
this new pain into the background, and during those days which were the first
days of spring, as I waited until Saint-Loup had managed to see Mme Bontemps,
I even enjoyed a few moments of agreeable clam in imagining Venice and
beautiful, unknown woman. 
As soon as I was conscious of this, I felt within
me a panic terror. This calm which I had just enjoyed was the first
apparition of that great intermittent force which was to wage war in me
against grief, against love, and would ultimately get the better of them. This
state of which I had just had a foretaste and had received the warning was
for a moment only what would in time to come by my permanent state, a life
in which I should no longer love her. And my love, which had just seen and
recognised the one enemy by whom it could be conquered, forgetfulness, began
to tremble, like a lion which in the cage in which it has been confined has
suddenly caught sight of the python that will devour it.
(Marcel Proust, Albertine Gone, ed. & tr. Terence Kilmartin, Chatto & Windus, London, 1989, p. 30; also in In Search of Lost Time, The Modern Library edition, Vol. V, p. 603)