How has the decision affected the traveler's life in the years that have passed? Quote the line(s) from the poem that support this

The narrator does not actually describe his life after he makes his decision in the woods about which road to take. He describes the two different roads, the appearance of each, his feelings about having to choose one, and the realization that—despite his curiosity—he will likely never be able to experience wherever the other road leads. In the final stanza, the speaker describes what he plans to do in the future: he says he will tell people that he once came to a fork in the road, he "took the [road] less traveled by" other people, and this choice "has made all the difference" in his life. However, all the evidence he's provided confirms that there really isn't a road less traveled. He has already said that

[...] the passing there Had worn [the roads] really about the same, And both that morning equally lay In leaves no step had trodden black (lines 9-12).

In other words, about the same number of people have traveled each road (they are worn "about the same") and neither have been walked that particular morning (the fallen leaves have not been walked upon). Therefore, we cannot really know how the traveler's decision has affected his life: he only tells us what happened at the crossroads and what he plans to tell people in the future.