Before we get into topnotch philosophical quotes, just one more treat with our favorite fictional philosopher: Professor Levy in Woody Allen’s Crimes and misdemeanours. He explains the inherent paradox that exists in love.

What do philosophers say about love?
To be clear, although philosophers distinguish many forms of love, like the love of ideas, what’s of interest for us Love actually enthusiasts here is merely the love between a man and a woman, a man and a man, a woman and a woman, or even between a human and a non-human being - friendship excluded of course.
Hegel, Fragment on Love, 1798
Love seeks out differences and devises unifications ad infinitum; it turns to the whole manifold of nature in order to drink love out of every life. What in the first instance is most the individual’s own is united into the whole in the lover’s touch and contact; consciousness of a separate self disappears, and all distinction between the lovers is annulled.
Nietzsche, Thus Spoke Zarathustra (1883-85) - On Reading and Writing
There is always some madness in love. But there is also always some reason in madness.
Plato, Symposium, c. 385–380 BC - Aristophanes
The original human nature was not like the present, but different. The sexes were not two as they are now, but originally three in number; there was man, woman, and the union of the two, of which the name survives but nothing else. Once it was a distinct kind, with a bodily shape and a name of its own, constituted by the union of the male and the female: but now only the word ‘androgynous’ is preserved (…)
Once they were split in half, they clung desperately to their other half until they withered and died from weariness and hunger. Zeus had compassion on these wretched creatures, and made sure their genitals were functioning properly so that they could fit together. This is why we feel love for others: we are literally searching for our other halves.
… friction of innards and convulsive ejaculation of mucus.

…only love has the power to forgive. For love, although it is one of the rarest occurrences in human lives, indeed possesses an unqualed power of self-revelation and an unequaled clarity of vision for the disclosure of who, precisely because it is unconcerned to the point of total unworldliness with what the loved person may be, with his qualities and shortcomings no less than with his achievements, failings and transgression.
Love, by its very nature, is unworldly, and it is for this reason rather than its rarity that it is not only apolitical but antipolitical perhaps the most powerful of all antipolitical forces.
It’s quite an undertaking to start loving somebody. You have to have energy ,generosity, blindness. There is even a moment right at the start where you have to jump across an abyss: if you think about it you don’t do it.
Being deeply loved by someone gives you strength, while loving someone deeply gives you courage.