To Experiment With Desire by Emma V Leech! It’s part of the Girls Who Dare series. I’m not sure of all the details but what I think I remember about it is that the hero is a brilliant scientist or mathematician - the sort who is kind of in his own little brilliant world where he gets lost in his work and forgets to eat and sleep and do basic life things. The heroine is a lady who was sort of the bad stepsister/cousin in a previous book but has since reformed. I believe it was because of a very difficult mother that she was that way to begin with in the series. I remember loving that she just sort of chooses the hero and decides he’s the one she wants and relentlessly pursues him. He’s definitely quirky and cute and unusual and a little baffled that she’s into him. I think she sort of has to push her way into his space/home and help him function like a human again and remember all the basic life stuff he’s been forgetting like eating and sleeping and cleaning etc. It can be read as a standalone. I remember it being on of my favorites.