When you give your soul to a person, thinking they will never hurt it. Trust is when you believe with your entire heart that a person will not turn you around and stab you in the back.
Knowing that no matter what happens, that a person will always be there for you. The most important thing in a relationship. Something worth fighting for. Our greatest power and weakness.
"I trust you, please don't make me regret it."
"You wont regret it, I promise."
Treating somebody as a friend doesn't mean you trust them, it means you don't think you're better than them, and you don't think they're better than you.
The guy would treat people as friendwhether he trusted them or didn't trust them.