I'm pretty sure it's a hentai manga since I had to crop out the inappropriate parts to post it here. I found the image on tumblr but was never able to find the actual manga. Does anyone know where it's from?

I think i saw this, but i don't remember the name, only the plot. It's hentai. The boy is a young lord and the next leader of the village, but he wants to run away with the girl. But they had been found out. His father or grandfather makes a bet if the girl can hold out a week then they can go. After that the girl is raped multiple times by the villagers and made to succumb to pleasure. The old man say something like her blood made her like this, and the boy goes away. So it's an NTR mind break story.
I remember it because it made me think, that after the end of story what have i done, be the next lord and kill all the men, or something like this.

Google says Inbi Temptation, which is a collection of oneshots. The oneshot in question is as kainord says, your standard-issue NTR.

Too short and 'cookie-cutter' to rage at. Then again, I don't rage at NTR to begin with; I find them hilarious.