I've had several shifting pairs of girls, and they all seem to have their own relationships, though I would consider them all bonded in that they got along and looked for one another if one was away for any length of time. My first pair, Linney and Frenzy, squabbled a good bit, but didn't fight. Linney was extremely dominant and Frenzy would occasionally challenge her and get put in her place, but besides some rumblestrutting and the odd 'out of my way' snap at the neck from Linney, they were good. Frenzy had health issues and passed away fairly young, and I will always remember Linney coming over and grooming/nuzzling/licking Frenzy's face when she got home from the vet. I think she was trying to remove any unfamiliar smells from the vet, as well as welcoming her back. After Frenzy passed away, we got Sundae and had Linney and Sundae as a bonded pair for about four years. Linney was still a very dominant boss pig, but there was less rumbling because Sundae was much more laid back and didn't challenge her. Linney didn't like sharing the pigloo at night so they slept separately, but they coexisted happily together until Linney passed away at age six. Sundae was very anxious and unsettled when she lost Linney, so she obviously felt a bond to her and missed her badly. After Linney passed, we came home with Hadley to live with Sundae. Hadley is the dominant pig, despite the fact that when we got her Sundae was probably twice her size (Sundae apparently was born to follow and doesn't want to be the boss, ever!) However, Hadley is a lot more of a laid back dominant pig than Linney was, and the two of them get along well and snuggle more than Linney and Sundae did. I've just noticed that Sundae gets literally stepped on a lot more because she is almost five years old and fairly sedate and Hadley is about six months and gets very bouncy/excitable, and if Sundae is in the way she literally runs right over her to get where she is going! At any rate, they all had their own foibles as pairs and their own relationships, but I would have considered them all bonded pairs. I would say as long as there is no fighting and they tolerate one another there is a bond there, but the relationship itself may change, wax and wane, over time.
