In episode 18, Subaru gives up on basically everything and suggests to Rem that they run away to live a happy life in another country. However, he knows that...
they will all die if he doesn't prevent Emilia's death.
I know that Subaru has suffered a lot at this point and he's broken and hopeless, but surely he would know he would only get three days of happiness AT BEST before he dies again and starts over again. So why did he even think this was an option?