Hey, Les! Happy to hear you like to reread chapters. So do I. As far as how Lucas meet Boone, he was the reddish-haired cowboy Coy mentioned he saw Boone kiss in "Sidewinder". Coy saw him but didn't actually meet him. And later in the story, Boone mentions Lucas again, in a conversation with Coy while they are traveling to Larkspur. I don't like giving away spoilers, but I guess it's okay in this case. Boone had his one experience with Lucas before Lucas moved on.
Much later, Lucas realized he loved Boone, so went looking for him. He found him in Larkspur, but saw he was too late, that Boone was with Coy, and never went up to even say hi. It's why he moved on to Bearpaw and bought some land. Hope this helps, friend.