Ron came to bring back her glasses that she left at the restaurant. In the words of Chris Rock "At what restaurant do they bring you back something you left? I want to eat there! You can leave a new born baby, and they will put it in the coat room". IOW, they WERE lovers.
It's a safe bet that most waiters would leap at the chance to personally return a celebrity's property.
Though that kind of stuff can be hard to figure out and generally only the killer knows for sure what happened at any murder (and frequently they're pretty zoned out and don't know themselves). But regardless of the order of the killing the indication is that while Ron thought he was in danger (ie was not completely unexpecting of an attack, in a defensive posture) he did not realize just how much danger he was in and was clearly blitzed too hard to be able to defend himself. That kind of situation usually means there's some level of trust involved (misplaced obviously), this trust could be the way normal law abiding citizens trust the police. But then we have to go back to the way Nicole was mutilated which is classic spousal murder facial mutilation.
Really to me Ron is very secondary in all of this. he most damning evidence all revolves around Nicole. The fact that OJ did beat her, the bizaar behavior he had towards her in the weeks prior to the killing, the mutilation, the bizaar behavior since the killing, the really twisted and messed up stuff he's said about her since then. Basically from where I'm sitting OJ was going to kill her, his violent behavior was increasing in both frequency and brutality, his aberant behavior was moving him farther away from normal society, and it was all focusing on her. If he didn't it's because somebody beat him to it, one way or the other Nicole is dead by now and most likely dead by OJs hands.