。。
Life is despair. That's how I see it.
Literal
Life [definitional-とは] despair [literary-copula-である]. I [topic-は] this-way am-thinking.
Two stark, philosophical declarations. とは in 人生とは is the definitional topic marker — 'as for what life is.' である is the literary copula, giving the statement a written, manifesto-like weight. The second sentence, 僕はこう考えている, uses こう ('in this way / thus') to reference the preceding claim. 僕 (soft masculine 'I') combined with the blunt philosophical assertion gives the whole passage a young-intellectual, almost novelistic tone.