I'm seeing a lot of projection going on, assigning feelings to perp and victim for which there is no evidence available to us. The truth is we don't know how HE felt about SM, how SM felt about HE, how either of them thought about or felt about the affair. This is going to be a mystery at least until some sort of litigation happens and there is witness testimony. Or, we may never know. We don't only know "very little," we know nothing at all. Who here actually knows these people?
We'll never know exactly what went down at that boat launch area, moment by moment, unless there's a confession. We'll probably never know exactly "why" either unless there's a full confession.
The state doesn't have to prove the "why" (i.e. motive), they also do not have to prove the moment-by-moment movements, and neither is it required that they prove how HE felt about SM or how SM felt about HE.
The rest is throwing spaghetti against a virtual wall to create a narrative and assign emotions and feelings to each of the players based on imagination.