Is the rest of this also Girl's-Love-focused, or does it divert into some weird story about aliens?
This is, first and foremost, indeed Girl's-Love and everything else is secondary. It's plenty gay on Adachi's side and how gay it turns out depends on how gay Shimamura lets it get, at least that's how I see it.
It's a VERY slow burn, from what I understand. Eventually Shimamura succumbs to her gayness, and they do eventually end up going out with each other. But that happens like in volume 6 or 7, so it's a ways down the line. This was just volume 1...
I try not to let myself get too spoiled about things beforehand, which is kinda dumb of me, but it's whatever. lol