I feel like Yena's "It's rare to see just the two of ya." is definitely some weirdly meta admission by the author that, yeah, it's just one bullshit coincidence after another to ruin any potential developments between the only two humans at this school. Then the fucking snake happens, as it to completely confirm it.
...geez, why can't these idiots just embrace getting into some big polyamorous amorphous blob of relationships? Seriously, we've seen multiple harem setups (or the reverse), and it's been pointed out that humans are actually pretty weird for being monogamous. (Or at least pretending to be monogamous.)