besides the fact that i think harry looked at hermoine like a sister, i also think he knew that if ron took an L on hermoine, that he would off himself. theres parts in the book where ron is being a jealous fakkit, if harry woulda snatched his bytch right there, ron was gonna commit that.
all jokes aside though, the point about ron and hermoine hanging out in the summer without harry is a good one, no way to know how close they were getting right there.
the fact that harry was so famous is definitely one of the reasons he went with ginny. he knew her forever basically, so he knew she wasnt just latching on to him for his fame. that kind of thing goes a long ass way.
the way my man neville bossed up by the end, he deserved to smash luna.