Loneliness and friendship. The yinrih have all the makings of alien precursors in a galaxy where there are seemingly no other alien races to precede, and there's a melancholy that pervades their culture as a result, especially given the dominant religion has as its core tenant the existence of other sophonts dwelling among the stars and the yinrihs' duty to find and befriend them.
Also, in a species with no eros, the practical functions of a spouse, such as care when sick, emotional support, pooling of resources, etc. are sought in one's circle of friends. Yinrih grieve the loss of friends deeper and longer than humans typically do, which is a problem when the one species of starfolk they finally find only lives a tenth of their lifespan.