A Reylo type relationship required Kylo to be less evil in TFA and for Rey to join Kylo in TLJ. It’s infeasible to squeeze it into IX at this point with how the previous 2 films have been.
It can still be included. The Force Awakens gave a subtle beginning, and The Last Jedi was much more clear in the representation of their relationship. It’s actually quite impressive how Lucasfilm was able to do so much with their relationship with such little time in Episode VIII. Plus, the film left off with an open ending as to whether Ben will remain on the Dark Side, or return to the Light.