Should only adverb come after "how" to express surprise like this?

It seems like "something" is not necessary here. Can I just say "I had to go like this"? What's the difference?

"Something like" is a phrase that means "similar to". Therefore, "something like" is used when referring to something that is an approximation, whereas "like this" is used when referring to something exact. Ex: My dog looks something like this dog, except my dog is shorter. Ex: My dog looks like this dog, they are the same breed.

It's very hard to accept the concept of "we are (= equals) society" here. If this sentence was "we are living in a dark-deprived society" or "we are the member of a dark-deprived society", then it would be easier to understand, but how come "we" can be a "society"?

Society refers to all the collective individuals living within a fixed unit, such as a country. Thus, the plurality of individuals means that "we" can be used. Society is also referred to by "it" in many instances. Actually, "we are living in a dark-deprived society," "we are members of a dark-deprived society," and "we are a dark-deprived society" express the same idea - that as a society (as a whole, as a group), we are deprived of the dark as there is always light around us. "We are a dark-deprived society" is direct and concise, and also expresses the speaker's idea clearly, so he has used it. Ex: We are a money-obsessed society. Ex: We live in a money-obsessed society.

Is the word "failings" a gerund in this sentence?

"Failings" is actually a noun here, used to describe one's weaknesses or shortcomings. "Failings as a man" here means "weaknesses/shortcomings as a man." Ex: Being unable to forge close friendships is one of my personal failings as a person. Ex: I feel like my fatal failing is my lack of ability to trust others.

Is “water” a verb here?

Yes. Water is used as a verb in this sentence. To "water" means to supply water to plant, or soak with water. Ex: You need to water rosemary every once a week. Ex: The gardener waters the garden twice a day. The verb form of "water" can also be used to supply water to animals for drinking. Ex: I need to water the cows.

Who is "George Custer"?

George Custer was an American military officer and commander during the Civil War. He was known for fighting against the Native Americans during this time and was killed in the Battle of Little Bighorn.