Esurabaru's Favorite

I don't remember a lot but it was a really sad story about this girl who sold herself and she meets this boy who I believe was sick and i think they made a promise where she wouldn't sell herself again but then she finds out he's super sick and can't afford surgery so she starts 'working' again and ends up with the money but also gets std? She dies at the end and he survives and learns about what happen? Please help!!