Well thing is with birds, if they have some sort of defect, injury or illness, they'll often be picked on by fellow flock members. This is because, as prey animals, the weaker one in the flock will be an easier target to predators, and so they try to drive the weak one out. That's probably why Rio's mate started attacking him.

What Carolyn's trying to say, is that he's still in a group, regardless if there's other lovebirds or not, so you really don't have to get a another lovebird, since he's perfectly happy with the birds that he's around already, especially since they seem to accept him, regardless of injury.