In France, it's called Amour courtois (courtly love). A topic in Medieval literature. But actual love romances aren't even considered as books. Somehow, it's a fascinating category, with almost 99% female readers. A very interesting object of study, almost a revolution in a new field of investigation.

In the Communication discipline, you can find this research as a subset of Relational Communication called "Romantic Communication." There's a lot of theories there, from Knapp's Relational Development Model, to Relational Dialectics, to Social Penetration, to Uncertainty Management to Social Exchange.

I really like Knapp's model that starts at integration and ends with termination, which is applicable to friendships as well as romantic relationships. An overview is here: https://www.communicationtheory.org/knapps-relationship-model

I also like these pieces in particular:

Baxter, L. A., & Pittman, G. (2001). Communicatively remembering turning points of relational development in heterosexual romantic relationships. Communication Reports, 14(1), 1-17.

Knobloch, L. K., & Carpenter-Theune, K. E. (2004). Topic avoidance in developing romantic relationships: Associations with intimacy and relational uncertainty. Communication Research, 31(2), 173-205.

Theiss, J. A., & Solomon, D. H. (2006). A relational turbulence model of communication about irritations in romantic relationships. Communication Research, 33(5), 391-418.

Hall, J. A., Carter, S., Cody, M. J., & Albright, J. M. (2010). Individual differences in the communication of romantic interest: Development of the flirting styles inventory. Communication Quarterly, 58(4), 365-393.

Hope this helps!

~ A

If we call it, provisionally, as courtship behaviour, it could include, for instance, issues like why certain types of specimen are found to be irresistible and why certain others evoke no response.

Look at research on attachment as well as some of the recommendations above: Chapter Attachment and Relationships

Or the sociology of love and emotion, e.g. Illouz.