Guts transformed into the Black Swordsman after the Eclipse, gaining strength and weapons to hunt down Apostles. Despite his upgrades, Guts would still not be able to defeat Griffith and the God Hand, as they were beyond human reach.
While Guts' physical strength is very impressive, he cannot compete with someone like Griffith. He did receive the Berserker Armor, but it isn't enough either. At best, Guys can defeat Griffith's generals in combat.
Zodd was impressed by both of them, even if he still won in the end. Everything about this scene depicts Griffith and Guts as equals on the battlefield. However, Guts would grow strong enough to beat Griffith in a duel. This was proven when he left the Band of the Hawk to follow his path in life.
Power Disparity: Griffith's transformation grants him immense power, making him a formidable opponent. Guts, on the other hand, is a lone swordsman with limited resources. The power disparity between them makes it difficult for Guts to directly confront and defeat Griffith [1].
Griffith sees some of himself in Guts, so he thinks of him as someone he can relate to. He could even see him as an equal because of their similar drive. The main takeaway from Griffith's feelings for Guts isn't what they were but rather how they impacted him.
If you saw the original Berserk anime series (1997). Casca never loved Guts. She only loved Griffith from the beginning. But when she did not get Griffith in her life and realized that he is out of her reach, she started leaning towards Guts as a substitute.
When Guts left the band, Griffith was devastated and acted terribly rashly. Griffith acted in spite and wanted to take everything Guts held dear, and that's why he slept with princess Charlotte. As a result, he was tortured and maimed.
While he did save Casca from falling rocks and has not made any attempts to kill either her or Guts despite the swordsman opposing Femto, it is heavily implied that this is due to the influence of the demon child, who holds a strong bond with both of its parents.
Following her mind being restored, Casca returns to being the person she was before the Eclipse. She is shown to have been aware of everything that happened during the years she spent being in her previous state, recognizing Farnese immediately upon seeing her, and tearing up with a smile when asked about Guts.
After giving his life to save Casca again as well as getting his revenge on the man who took everything from him, Guts will finally receive a bittersweet end, dying happily and peacefully knowing that Casca is safe and that all of his hard work and suffering weren't for nothing.
But Guts leaves the Band of the Hawk after defeating Griffith in a duel, having overheard Griffith's ideal of friendship and seeking to follow his own dream.
If Guts became an Apostle, then it'd ruin any chances he'd have against Griffith/Femto and the rest of the God Hand. Currently, he still doesn't have much of a chance, but Ganishka has shown it doesn't matter how powerful you are as an Apostle, you're still a servant to the God Hand. It's in their instinct.
At first, Casca had an attachment to Griffith, admiring him for the persona he had set on. When Guts arrived Griffith had basically focused all of his attention on him, which brought out Casca's jealousy towards Guts.
It's very likely that when the Skull Knight later tells Guts that his journey is almost over, the mysterious undead warrior was correct; Guts was destined to end his quest consumed by hatred and revenge, so far as Guts never saw Griffith's face again.
Guts may be the strongest swordsman in Berserk, anime and fantasy as a whole. For now, the only beings he can't kill on sight are the nigh-immortal God Hand and Griffith.
Griffith was once Casca's personal idol and hero, and every other member of the Band of the Hawk saw him the same way. For years Casca wanted -- and hoped for -- her relationship with Griffith to be something more. Years later, she finally realized it was never meant to be.
While Griffith must bear the weight of his own decisions, Guts had every chance to prevent his friend from becoming a true terror. Griffith was poised to give up on his dream thanks to his friendship with Guts, and it was the dissolution of their relationship which transformed him forever.
The child was conceived when a newly returned Guts had sex with Casca, impregnating her. During the Eclipse, Griffith offered the Band of the Falcon to be reborn as the God Hand member Femto.
Guts' departure meant losing a valuable comrade who played a crucial role in their victories [1]. Jealousy and Insecurity: Griffith's feelings towards Guts and Casca were complex. While it is debatable whether Griffith genuinely loved them, he did value their contributions to his dream.
Due to his similar appearance to Frikka from Berserk: The Prototype, it became a meme and some even genuinely theorize that Griffith was originally going to be a woman before Miura decided to make him a male character.
Power and Control: The sexual assault can also be seen as an expression of power and control. As Femto, Griffith possesses immense power and authority, and the attack on Casca is a way for him to exert his dominance and assert his new position as a member of the God Hand [1].
Judeau was able to notice that Charlotte was in love with Griffith. He was perceptive enough to see that, with Griffith's anointment as White Phoenix General, the only method of further ascension left for the Falcon was through the betrothal of Princess Charlotte, leaving no room for a devoted Casca at Griffith's side.
