Jasper's epilogue is one of the hardest things to achieve in the game - you not only have to succesfully romance him (a challenge) you also have to get all legendary outcomes - this gives an achievement at the end of negotations
you will know you succeeded at legendary outcomes if you see the following lines in the endings:
"And so, Arland and Jiyel slowly transformed one another and in doing so also changed the world."
"And so began a legendary golden age for both Hise and Corval."
"And thus began a time of legendary change for both Wellin and Skalt."
"Although it once seemed an impossible transition, it is not long before former enemies manage to find themselves reluctant, but accepted allies working together to change the fate of a rebuilt Revaire."