The one that invited the other as their gues or if the person insists on split then split it.
Imo it should be the stem student.
Play rock, paper, scissors - best of 3, loser pays.
Why does there have to be a hard and fast doctrine for this?
Split the bill unless one person is in much better financial straits than the other.
Whoever made the invite for the date should be willing to pay for the date.
If the person who agreed to go on the date wants to split the bill, that's fine.
But if the invite issuer claims to have forgotten their wallet or asks for a loan, that should be seen as a big red flag.
If you were friends before then split, if he’s asked you out he should at least insist on paying full (it’s your call if you wanna split. I’m sure he’d be expecting to pay full though), if you asked him out he’d probably insist on paying for himself at least and maybe even you if he’s had a good time.