Animals develop and maintain friendships just like we do as humans. They need socialization beyond humans. These relationships help them learn and maintain boundaries and cues, and help with emotional support.
They develop love and strong bonds with others. Many talk to me about their friends. They make each other happy. They comfort each other. They offer emotional am support when one is injured or sick, old or dying. They groom each other. They play together. They become family. They take care of each other. When they see another in need emotionally or physically they feel empathy, like we do. These relationships run deeper than most humans realize.
Some animals are not friendly with others because of past trauma but the majority need relationships in some way with others, so they can thrive. There relationships with others is as important as their relationship with us and as important as our relationships are with other humans.
As humans, we can help encourage friendships. Sometimes humans aren’t enough. Sometimes they need other animals to truly thrive. 
Now when their friends leave and never return due to rehoming, sale (horses), or death, expect to see the effects of a broken heart – or a lonely/confused heart. It is confirmation of the depth of the relationship
