Why did he considered Guts the only one that made him forget his dream?
It's just my opinion, but this hasn't been fully explained yet
Westerners have difficulty understanding this dynamic since our culture is very different. In Japan, there is a massive focus on hierarchy and respect, a lot of power dynamics, and sometimes friendly rivalry, which is hard to explain. You can see some examples of that in Ryu x Ken from Street Fighter, Sonic x Knuckles from Sonic, Ryo x Robert from Art of Fighting, Sora and Riku from Kingdom Hearts, etc. You can even see some of that in Zodd x Guts. Zodd had the opportunity to kill Gutts back in Vritanis when they fought Ganishka, but he decided not to do it. He even attacked the other apostles who tried to hurt him.
What happens to Griffith is that he sees Guts as the complete opposite of him, and becomes fascinated with him. Guts had no dreams, or goals, and was completely free while Griffith led a very rigid life that had to conform to his dream. He could not understand how a person could live without a dream or a purpose.
Not only that, but Guts was pretty good at combat, being the only one to rival his skills and eventually, surpass him.
As the Hawks ascended, Griffith realized that Guts was a fundamental paw to help him achieve his dreams, but he also began to sense he was developing strong feelings towards him, feelings of respect, friendship, care, and love (not in a homosexual way, IMO).
When Guts left, Griffith was shattered, for Guts was the only person that he ever truly cared for, and he had a mental breakdown, believing he could never achieve his dream without him, and also hating the fact that he was so affected by the departure of a single person.
That is my opinion, as to why it was never about homosexuality.