That's right. I forgot about that scene. Though Luke did NOT murder Ben Solo, he just thought about it for a MOMENT and then came to his senses quickly.
Again, never liked the notion of using Anakin's lightsaber. Fine, Rey accepts it from Maz Kanata. Still don't know how it was retrieved from Bespin. That should have been it. Keep in mind that it is part of a Jedi's rite of passage to find their own Kyber crystal and build their lightsaber. Remember the deleted Luke Skywalker scene from ROTJ.
Luke should have "battled" Kylo Ren with HIS own green lightsaber in TLJ.
Well, we all know Rey appropriated everything from Luke, so.....