Delirium (Delirium #1) by Lauren Oliver

There was a time when love was the most important thing in the world. People would go to the end of the earth to find it. They would tell lies for it. Even kill for it.

Then, at last, they found the cure.

Now, everything is different. Scientists are able to eradicate love, and the government demands that all citizens receive the cure upon turning eighteen. Lena Haloway has always looked forward to the day when she'll be cured. A life without love is a life without pain: safe, measured, predictable, and happy.

But then, with only ninety-five days left until her treatment, Lena does the unthinkable...