Do atheists believe in the existence of friendship?

[Astreja]

But specifically, it is dopamine, serotonin, and oxytocin (mostly oxytocin) responsible for trust.

In this case, I bet those who can have these chemicals in their body are rare on earth.

No, those chemicals are in everyone's brains. They're neurotransmitters. Our brains function electrochemically, and our moods and emotions are literally chemical reactions. The levels of the neurotransmitters in our brains can be high or low, and can be influenced by genetics, by environmental factors such as stress, and by pharmaceuticals (e.g. dopamine agonists, SSRIs or intranasal oxytocin).