Even though they were ideological opposites, they liked each other personally. Their families socialized quite a bit, they traveled together (you haven't seen the photo of the two of them on the elephant in India?), they both enjoyed opera and attended together frequently. In fact, a modern opera was even written about their friendship.
I sincerely doubt their friendship had any impact on their voting records, but I'm sure Ginsberg is absolutely gutted.
Also: Scalia introduced Kagan to shooting, and they went hunting together on occasion.
Come to think of it, one of my very good friends is a lefty. A Bernie supporter. We socialize all the time; we just don't get into politics.
It’s gotten harder and harder to maintain friendships that cross ideological lines but I still have a few myself. Attitudes have hardened considerably, though, to the point that politics just aren’t discussed.