Trust is something on which a relation survives, sustains and simply thrives. The relation could be with a spouse, sibling, some friend, colleague or anyone. Besides empathy, understanding, loving and caring attitude, trust, too, happens to be one of the imperative ingredients in the recipe to successful relations.
In fact, trust is as central as one of the cardinal foundation stones of a massive building. Or, one of the concrete columns, supporting a cupola-like domed structure. Or, one of the strong threads, woven into the relation fabric. Or, one of the essential elements, in the composition of a potent drug.
Now, when we say we trust a friend or a relative implicitly, what exactly does it connote? It means you are confident that the person, who is trusted, unconditionally/genuinely likes you, the way you are, without being judgmental or opinionated, just as the way you'd have accepted him/her, with warts and all. And, identifying your successes/sorrows as hers/his, s/he is always beside you, with unremitting tacit support, in moments of both tears and triumphs, unlike the 'fair-weather friends', who stick to you only out of some personal benefit/mileage. More importantly, the trusted person has bountiful loyalty, more behind your back than before you! Which means, when your detractors are trying to denigrate you, with deadly slander missions, s/he'd instantly dive to your defense, even if it means distancing herself/himself from others. Apparently, even a speck of self-saving or self-image-enhancing tactics/diplomacy is emphatically not in her/him.
Next, the trusted person never backbites, or betrays you by committing breach of trust. Rather, s/he battles hard in not bringing any kind of blight to your image. And, with the person, trusted, you are totally yourself, being able to speak your mind out, without fearing repercussions of what you'd have uttered, being misconstrued, magnified, or morphed and leaked out in misrepresented form. Finally, the trusted person is the one, who, too, is seldom secretive, and has the same amount of trust in you, so as to share all her/his feelings, emotions, and every single thought, just as you do. No wonder, if this trust gets extinguished, it doesn't take much time for even the sturdy relations to crumble, collapse, and crash down.