(note: Though it is unlikely to specifically matter within this review, I am specifically discussing the director's cut versions of these episodes because they feature much more content than the cheaply-made TV broadcast version. I suggest you skip them in your viewing as well.)
In the last set of episodes, we watched as Shinji's world fell apart, and now the world crumbles around him. Shinji's closest friends lose themselves in a sea of depression, and those who dare to be stable are met with death.
Episode 21"The Birth of Nerv/He Was Aware That He Was Still A Child" is an extensive flashback of Gendo's backstory, and features lots of cryptic info on the MYSTERY of the series. This episode is actually my favorite of the entire TV series, giving Gendo and many other characters the element of pathos that defines their roles for the final act of the story. We see Gendo in his prime, friendly and happily married, and watch as he falls apart, morphing into the monster of a man who calmly traumatizes his own son. We soon realize the Gendo is what Shinji might become. At the end of the episode, someone dies and someone else falls apart, and the very idea of Eva being a normal robot show falls apart. Now the series progresses to show Rei die bravely in combat, replaced by an emotionless doll calling herself "the third one", Ristuko revealed to be psychotic, and Asuka literally get mentally defiled. Truly great merchandise fodder.
At this point, Shinji is, of course a wreck. It is only natural he find someone to turn to. By the way, that sound you hear is a million fangirls squealing. In Episode 24 "The Final Messenger/T