They like family. I don't think Spartan-IIs are capable of romantic love. They are mentally engineered to be the best soldiers, survival and fighting is all they know. Behind that they do actually care a great deal for people within their circle. Such as Halsey, Mendez and anyone that has earned their respect. This is dependent on the individual. For example, Linda is more cold. While Kurt is more social and less introverted. It depends on character. But they do ultimately care about other Spartan-II in particular, especially since so many are being "MIA"d it makes each surviving S-II more important. Since Kelly and John have been on the same team since their inception to Blue team with the exception of Sam. They share a arguably closer bond. It's like a childhood friend thing that cannot be recreated, it's irreplaceable.