Oltarin: The Horse Clans Colony: Aledan Series Book Two (Aledan #2)

Hankura and Chelle continue their life together joining the crew of the Searching Star, an exploration ship with a mission to find new worlds for colonization and reconnect with lost colonies. Their lives are on an intersecting course with the horse clans of Oltarin a lost colony in the midsts of a 500 year old blood feud primarily between the mountain clans and the lake clans. Their society devolved from space faring into rival clans who rode horses and fought each other with swords, knives, and crossbows.

On his way to send the message from the ancient shuttle, Brandt McKell, son of the Mountain clans' chieftain rides to help a lone rider being chased by four renegades. He can hardly believe his luck when that rider turns out to be the daughter of the Lake clans' chieftain---his deadly enemy. It's not exactly love at first sight, but sparks fly and passion ignites.
It's up to the crew of the Searching Star to determine if these people can settle their differences and claim their rightful place in the Federation.