Why did the creature stop taking food from the cottagers' store?
In Mary Shelley's novel Frankenstein, the creature undergoes a series of deep epiphanies from chapters XII-XVI. These are a result of the creature becoming closer to the cottagers whom he observes from his hiding space. However, it is in chapter XII where we find the creature really connecting with the cottagers; the Delacey family.
Among his observations, the creature begins to realize how poor the DeLaceys really are, and how this affects them.
Their nourishment consisted entirely of the vegetables of their garden, and the milk of one cow, which gave very little during the winter, when its masters could scarcely procure food to support it. They often, I believe, suffered the pangs of hunger very poignantly, especially the two younger cottagers; for several times they placed food before the old man when they reserved none for themselves.
Prior to observing the DeLaceys, the creature operates on survival mode and only looks after himself. He has not still experienced the feeling of community that he discovers vicariously through the dynamics of the DeLaceys. Once he begins to take notice, he also becomes introspective.
This trait of kindness moved me sensibly. I had been accustomed, during the night, to steal a part of their store for my own consumption; but when I found that in doing this I inflicted pain on the cottagers, I abstained, and satisfied myself with berries, nuts, and roots, which I gathered from a neighbouring wood.
Therefore, the creature goes through a form of social learning in which the good deeds of the cottagers inspire him to "give back" to the point of thinking on their welfare first rather than his own. This altruism precludes his true desire of being part of a supportive and loving environment.