The chapters of the book are numbered differently from edition to edition. In the one used on enotes, there are 3 volumes, each divided into chapters - this means there are 3 Chapter 5's in the book. I am assuming that you are using an edition with this same structure, and are referring to Chapter 5 in Volume 2.
In this chapter, the monster is relating to Victor how he spent months living alone in a cave, observing the daily life of a simple family of three in a nearby cottage. Through this routine, the monster learns about language, emotions, and interpersonal relationships. One realization that causes him bitterness is when he becomes aware of the difference between their physical appearances and his own. He notes, "I had admired the perfect forms of my cottagers...but how was I terrified when I viewed myself in a transparent pool...and...became fully convinced that I was in reality the monster that I am, I was filled with the bitterest sensations of despondence and mortification".
Despite this realization, and also despite his previous experience of being chased cruely away by villagers terrified and repulsed by his appearance, the monster begins to entertain the idea that he might be able to show himself to the cottagers, whose intitial disgust he would be able to overcome by his "gentle demeanour and conciliating words" and thereby "win their favour and afterwards their love".
In Chapter 5, the creature awakens after Victor injects it with chemicals. As soon as it opens its eyes and looks at his creator, Victor is horrified by what he has done. He immediately turns and runs when the creature reaches out to him. The creature, not understanding Victor's behavior, is hurt that his "father" would ignore and run away from him. He is left alone in the lab/apartment. After taking Victor's cloak to cover him, the creature ventures out into the world where everyone he comes in contact with runs from him in fear. It is the loneliness caused by his distorted looks that causes the creature to feel bitterness towards Victor Frankenstein, and later leads him to extract revenge on him.