Some rambling, based on this post by bthump ♥
Guts has always been so hungry for love and somehow, I think this has always been his dream from the start – to have someone want HIM, not necessarily his fighting skill whatsoever, but someone to appreciate him as a person, to trust him, to care for him, to watch his back, to just give a damn. I think Guts too had to make himself strong (just like Griffith), so he could survive in a world, where nobody gave horse shit for a young unfortunate boy. He sought love and attention in Gambino, he so much longed for the affection of his so called father, but he only ever got the opposite. Once Gambino died, Guts sort of lost himself, he belonged nowhere, so he would fight his way through the lands of the world and live day for day.
But then Griffith came along – a boy who knew nothing of Guts, yet was ready to fight to make him his. And even if Guts was irritated by it (and in his ears, none of what Griffith said probably made sense), I think in the end, we wanted to feel as if he actually belonged somewhere – and Griffith became this ‘somewhere’. Hell, it took one gesture to render Guts speechless and make him ‘obey’ (because I can’t believe he would have stayed, only cuz he lost a duel if he hated the idea of it)- it was a chance to finally get, what he wanted the most in the world – someone, who actually cared for him.
And after the Zodd encounter, we see him watch the moon, remember Griffith saying he has put himself in harm’s way for his sake and he is pondering if this is the answer he has been looking for all along. And the question is stated few chapters back, when we see the little Guts lie on the ground, after having killed Gambino – where is he going if the world has nothing good to offer? But maybe Griffith’s care and affection is this ‘good’ he longs for.
So he eventually leaves – because he wants to EARN his place by Griffith’s side – he isn’t simply aiming for a home, for warmth, he wants more – just like Griffith. Guts’s dream is, in a way, to stand by Griffith’s side and to be worthy of the care and affection Griffith has given him and not be eventually ‘left behind’ by the hawk, who always aims so high. Because by Griffith’s side is where he wants to be the most.
Another thing I would like to add is, that I don’t think Guts was unaware of Griffith’s feelings, I think in a way, he always knew. Which is I think he is rather shown to feel guilty, whenever Casca confronts him about it, than actually deny it. I think he felt guilty to be a special person to Griffith, even though he didn’t do anything to deserve it, while Casca made this her dream and fought for it. And when she told him about her life and how she came to fight for Griffith, the realisation hit even harder. He didn’t feel as if he would lose Griffith’s affection if he stayed, I think he believed he had already lost it and had to gain it back by becoming his equal.