Most people I know who went to BS, acronym or not, have very good friendships that carry through life. Living together during such a formative period creates deep, strong bonds for many.
Remember that a BS class is not that big, even at the larger schools, so a bond with BS friends is easily characterized as a bond with the school.
And BS do have reunions and events to keep alumni connected (and donating). That makes it easy to stay connected or to reconnect with old friends.