Oxytocin creates the good feeling of social trust. A mammal can lower its guard when trusted others are near. You might want this feeling all the time, but trusting everyone would not promote survival. The mammal brain evolved to make careful decisions about when to release it. Common enemies motivate mammals to seek safety in numbers, and their brains reward them with a good feeling. Neurons connect when oxytocin flows, which wires you to trust in contexts that triggered it for you before.
Touch triggers oxytocin, which is why it’s often called “the love chemical” or the “bonding hormone.” But reality is more complicated. In the state of nature, anything close enough to touch you is close enough to kill you. To complicate matters, your herd mates may embroil you in their conflicts and thus increase your survival threats. Animals are cautious about who they let close, and once they are betrayed, cortisol wires in an alarm response for the future. It’s not easy to keep that nice feeling going.
Primates invest energy grooming their troop mates, and oxytocin makes it feel good. But they make careful decisions about who to groom. They hope to build social alliances that promote their genes in the long run. But they’re disappointed sometimes, as their investments are not always reciprocated. But the primate brain survived by shifting its focus on new grooming partners. All of my books explain this in depth. A brief introduction can be found in the 5-day happy-chemical jumpstart (click the monkey/newsletter in the sidebar to the right for free sign up.) And check out this blog post, Independence v. Belonging: Riding the Seesaw.