The first lesson a Watcher learns is to separate truth from illusion.
This unveiling of Angel to discover his inner nature, reaching the darkness within, reaches a climax in Season 3 when Wesley kidnaps Connor, forcing Angel’s darkness to the forefront. Wesley finds himself confronted with Angel’s most violent self as Angel attempts to smother him while he’s lying in a hospital bed.
After having lost the Council, Wesley invested so much of his identity in helping Angel, believing that Buffy and Cordy were right: that Angel with a soul was good. The Prophecy that “the father will kill the son” forces Wesley to begin to see Angel as dangerous and this becomes a sort of self-fulfilling prophecy for Wesley as his actions force Angel’s monstrous self to the surface (a rage prompted by powerlessness and grief).
Wesley’s hopefulness becomes increasingly replaced by cynicism going forward. All these forces for good are masking inner darkness: the Council, Angel. And this realization pushes Wesley even further into his own potential for darkness — even back in Choices he was always willing to do what was necessary for the greater good (i.e., letting Willow die to stop the Mayor’s ascension). In Deep Down, when Wesley rescues Angel from the bottom of the ocean, it’s only Wesley who can find Angel in this monstrous realm deep where Angel’s trapped within his monstrous psyche because Wesley has broken through Angel’s mask and seen the monster inside. And having seen the monster, Wesley still believes he has a use, a purpose. Wesley doesn’t believe in Angel as an ideal Champion, but as a tool, a risk worth taking because Wesley’s considered the odds and he believes good will prevail, both in the world and within Angel. Believing in Angel means believing in the fight which Wesley’s dedicated his entire life.
Cordelia ends up knowing all about Angel’s entire life because she sees it on the higher plane. Wesley ends up knowing Angel, deep down, through this painfully wrought unmasking experience where Wesley is confronted by Angel’s immense capacity for darkness.
And having come to know Angel so intimately, this journey of Wesley’s discovery, of seeking the truth veiled by illusion, it leads to Angel robbing Wesley of this knowledge in Home, rewriting Wesley’s memories of his experience with Angel so that Wesley no longer knows Angel’s inner self on such an intimate level. Wolfram & Hart itself becomes another mask for Angel to hide behind, an elaborate con so that Angel appears outwardly evil in order to convince everyone he’s inwardly good. Layers upon layers, all so that he can hide from the people closest to him, rewriting their minds so that they cannot see him, cannot know him. Angel pretends he’s a good man pretending to be a monster so that his loved ones don’t realize he’s still got a monster, deep down.
This painful experience of knowing and being deceived plays out again for Wesley with Illyria — the fantasy love Wes feels for Fred in Season 5 itself becoming an illusion made possible by the mindwipe inHome (as opposed to Wes’ own dark connection to Fred in Season 4, i.e. Supersymmetry). Illyria and Angel and Wes — illusion and power and what it means to know evil, to be good, to embrace one’s inner self. Wes’ experience with these masters of monstrous illusion breaks him down. In attempting to know them, he loses himself to madness, depression and (arguably) suicide.
Wes’ journey in AtS, his stalwart determination to know truth and save the world, culminates in his giving into illusion with his dying breath, grateful for the solace that deception can offer. In that moment, when Wesley spans the chasm between living and dying, he finally understands what pushes Angel’s need to lie to himself. Whereas Wesley experiences a moment of living and dying, this is Angel’s constant: living as he’s been long dead, needing to lie to himself to believe he’s still human. Angel is a Champion and a monster.
Cordy and Wes experience parallel journeys, reaching similar destinations — self-sacrifice for the mission — for different reasons. Cordy seeks Angel’s inner goodness only to be consumed by the overwhelming illusion of his high and mighty persona as a Champion (her belief and cultivation of Angel’s Champion status is tied to the very same Champion status used to consume her). Wes seeks Angel’s inner darkness, as a Watcher must shine light into the dark to reveal and know, only to be consumed by the hopelessness and despair that comes with knowing that darkness. Cordy helps Angel wear the mask of Champion, her fervent belief in his Champion status never higher than when Wesley’s confronted by Angel’s inner darkness. The duality of Angel’s nature, the Champion persona and the monstrous inner psyche, are tempered by his two closest friends. Cordy’s faith fuels Angel’s capacity for goodness while Wesley’s search for what lies in the dark serves as a constant reminder for Angel to never forget because when Angel forgets the monster within, when he feels a moment of peace, he loses his soul. Cordy and Wesley’s journeys to discover who they know Angel to be, together, reflect the dualistic contradiction of Angel himself.
Ultimately, this journey to know Angel ends in tragedy as the only way to know Angel is to die. No wonder Angel doesn’t want intimacy, cannot have intimacy: the price of connecting with Angel for human beings is death. On an instinctual level, Angel must know this, that his fractured inner self comes from the experience of death, which is why he throws up barriers to keep people from getting too close. Not simply out of fear of losing his soul and becoming Angelus, but from this sort of existential agony that comes from knowing that he cannot be truly known when he’s dead and they’re alive. For the living to know him, they have to die.