Griffith agreed to have sex with the pedophile just to save his squad, he hated himself for having to do that and started self flagelating the moment Casca reminded him of it.
His relationship with Guts is in no way sexual, people say that just because of what he looks like, saying that two friends are in a gay relationship is a joke for half of the audience and a fetish for the other half (see Naruto and Sasuke, Saitama and Genos, etc).
Guts and Griffith are friends who see in one another a better man they wish they could be.
I think Griffith looks like a gay twink because of the japanese tradition of having a psychotic gay man as the main/prominent villain, such as Frieza in DBZ, the clown guy in HxH, Orochimaru in Naruto, etc.
I somewhat agree and disagree with you.
Griffith's feelings towards Guts were ambiguous with shades of romantic love in them, but Griffith himself was not self-aware of this.
Griffith, for his whole life until he met Guts, was consumed entirely by the pursuit of power and accomplishment, of greatness. He had no human connection. All of his associations and involvements with other people were motivated just by utility and power, he had followers, tools. Guts is the first person he ever meets that means more to him than that, but his relationship with Guts begins with Griffith acquiring him as another tool, another soldier to propel him to victory and power, so Griffith thinks of Guts as a tool all the way through even though Griffith's emotions towards Guts develop far beyond that of regarding him simply as a tool, Griffith's conscious mind doesn't ever realize or recognize this because it's never happened to him before, so it's unrecognizable to him.
Griffith's feelings towards Guts are part platonic love and romantic love, transcending both, and it would be very reductionist to describe it as either exclusively, they combine together to create something far deeper. I don't think either of them is gay in the sense of like some San Franciscan faggot going on Grindr to take as much dick as possible to get pozzed, it's not a generalized sexual attraction to just members of the same sex in general, but an extremely specific and narrow attraction to each other as people, their sexes being incidental. I get the impression that Griffith didn't have sexual feelings in general. Guts obviously does have sexual feelings towards women as sexual objects, but Griffith never gives any indication of having a physical sexual interest in anyone.
Gut's feelings towards Griffith are less complicated. It's much moreso a deep platonic/brotherly love and connection animated in parts by admiration, rivalry, and tenderness.
Gut's entry into the Band of the Hawk led to both Griffith and Guts developing the first human connections in their lives, Guts with the Band and with Griffith, and Griffith with Guts. Before Guts joined the Band, both of them lived purely for survival and power, fighting and killing constantly in order to not die. Guts was languishing in a chaotic and cold nihilistic void of violence, but meeting the Band and Griffith gradually started to show him that life could have a point, that being alive could have value, there was more to the world than just struggling to survive.
For Griffith, it almost showed him that there was more to life than power. For Guts, it showed him that there was more to life than mere survival.
Something worth noting is that despite Gut's impressive strength and combat ability, he never actually cared about power at all. Ironically, despite Gut's feelings being simpler than Griffith's, Guts was much more self-aware and understood himself better than Griffith understood himself, he knew he saw Griffith as his closest friend, that he cared about that, and he was willing to leave the Band of the Hawk to become equals with Griffith so that he could try, in some way, to truly be his friend. Griffith never even realized the nature of his feelings towards Guts, he automatically misunderstood his feelings towards Guts as just being his interest in having useful tools around him. It's really horribly sad. Griffith's obsession with power raped a beautifully pure emotion that existed between them to death and wiped it from existence.
One reason why Griffith's feelings towards Guts might have been more complicated and encompassed what seems to be all varieties of human love apart from sexual(Eros, due to Griffith generally seemingly indifferent to sex) is due to Griffith's complete and total arrogance and self-perception of superiority to those around him. He always put himself above everyone else in the Band of the Hawk and never truly connected with them, and so Guts was the sole focus of any human emotion that Griffith had, whereas Guts connected with both Griffith AND the members of the Band of the Hawk, and he didn't think of himself as superior to anyone, Guts doesn't think in terms of superiority and inferiority.

I've rambled too much, and my post is too long and I'm too lazy to read it to edit it and make sure that it's coherent, so it might be kind of incoherent and disjointed. Plus, we're going completely off-topic for the thread but whatever, don't think it matters too much because there isn't constantly stuff to talk about in regards to Synth.