This is very gay, just not explicit.
MC is overtly a highly manipulative dom, and his adventurer partner is clearly shown off as a sub. This is further strengthened by the obvious manipulation/grooming actions of the MC to push his partner into being subservient to him, which the partner seems to falling into quite easily.
The next hallmark of a gay story, the men drawn are FAR more attractive than the women. Hell, the merchant person looks 100% like an effeminate dude until the story suddenly tells you later that it was a woman all along, and I'm like WTF, no one would ever guess that from their appearance.
Third hallmark of a gay story, everyone, and I do mean EVERYONE finds the main characters (The dudes) to be highly attractive, regardless of gender.
And the biggest final tell, the men take the places that women would normally hold in the story. Every isekai story, adventurer guild receptionist? Pretty lady, here? A sparkly guy who immediately falls for the (dude) MC, the loner solo high tier adventurer that's oddly highly available to only the MC? Another dude, the eccentric who happily collects freaking teddy bears and gushes over pictures of other dudes? Another sparkly dude. Is there even one well drawn female in the entire manga that actually looks like a female? I highly doubt it.