It apparently can NOT be said enough because there are still folks who make this mistake, but you simply have to remove the habit of texting while driving from your psyche. There is never a time when it's more important to respond to that text than it is to pay attention to the road. Just think about how little time you are spending on the road, and you will realize it can wait until you get home.
If it is a drastic or emergency situation, then pull over and stop somewhere to text. Your text is not worth risking your (or another person's) life!