He also asked me if I loved his dad. I said “No, honey. I used to love him, but he’s not my friend anymore.” This unleashed a barrage of “why”s
You handled it brilliantly up until this point. This is where a child is trying to figure out how, if his parents could fall out of love with each other, could they fall out of love with him.
Also I wouldn’t say something like “Daddy’s not my friend” as he’s likely to repeat that to your ex.
Perhaps a better approach might be something along the lines of “sometimes grownups stop loving each other, but mommies and daddies ALWAYS love their children” or, since that’s not 100% true and your little smart cookie might notice that, you can just tell him “but I will ALWAYS love you” and point to how YOUR mom still loves you.
As for the comment about liking you best - normal little boy stuff. Not necessarily a sign of anything off, especially since he didn’t give any obvious issues as examples. Little boys love their mommies.
Oh, and stop watching dateline. Be aware, but so far your ex just seems to still be focused on “winning”. Once things are finalized I suspect things will calm down more.