While at first Adachi has thought and talked about Yamada as if all he wants is her looks, I don’t think that’s exactly the case, at least not anymore.
He only ever really acts and talks about that when he’s with his friends and all, but recently at least, when it’s just him or Ichikawa, he looks and acts a lot more…caring about her, especially with what this chapter told us.
Sure he definitely has sexual attraction, it seems he genuinely started feeling attracted to Yamada as a person around the time of that festival, and is probably only going on about her sexually to ‘look cool’, or it’s both.
But he is genuinely trying to at least open up truthfully to Ichikawa.
In the end, he’s just a teenager.