"Where there is love, there is often also hate. They can exist side by side." (18.128)
There's a fine line between these two seemingly opposite emotions, both rooted in passion, which explains why you can get so incredibly mad at someone you love.
"I loved [Valentine] too: He was my closest friend, and I was happy to see Jocelyn with him." (21.10)
Luke talks about his love for Valentine in past tense, so we're pretty sure he won't re-join Valentine's cause the way Hodge does.