Lucky Luke is ACE
I don't mean as in The Ace which he certainly is but a-romantic and a-sexual. there is a reason after all why that "poor lonesome cowboy" doesn't want to tied down. Lucky Luke and Lisette will become Official Couple.
They're childhood friends, and in terms of personalities are very similar to each other (Luke being a lonesome cowboy, while Lisette was raised on the farm), so it could be possible for Luke, that when it comes to Lisette, he could consider her exception to his opinion towards marriage and love. Young Daltons will appear in Kid Lucky.
Even though it will contradict how Luke meet Daltons in the original comics, this could still provide some fun origin story about how Luke meet his Arch-Enemies.