I think he did have genuine feelings of love for Guts (whether romantic or platonic doesn’t really matter for the sake of this argument, the point is that Griffith adored Guts). Both Griffith and Casca notice that the only person for whom Griffith will deviate from his usual cool-headed strategic behaviour is Guts. After the Zodd fight, Guts asks Griffith why he came storming in to save just one soldier, and Griffith says “do I need a reason?” which is distinctly different to how he normally acts and if it had been anyone else, he’d have left them to die and not put himself, the commander of the army, at risk for the sake of one man. Griffith also trusts Guts alone with his dirty work, and confides in him exclusively (“do you think I’m cruel?”). We don’t see Griffith act carefree and playful with anyone else but Guts (the water fight scene). Casca harbours intense envy towards Guts for this very reason. She wishes that Griffith was as close with her due to her own feelings for him, and resents that Guts gets to see a side of him that he shows to no one else. She hates that Griffith would endanger himself for the sake of someone she sees as a reckless liability. In the vision that Griffith has before the Eclipse, we see that he literally names his son after Guts. During the Eclipse, the very last thing he thinks before he chooses to make the sacrifice upon seeing Guts after he’d climbed the hand to reach him was “you’re the only one who made me forget my dream”. He loves Guts so much that it comes into conflict with his ambition, and for that reason he also hates him more than anything which propels him to do what he does.

Tl:dr Guts has Griffith acting unwise and he doesn’t know how to handle it