According to Wikipedia (http://en.wikipedia.org/wiki/Trust_(sociology)) Trust is a measure of the belief in the honesty, fairness and benevolence of the other party. It is also dependent on the competence of the other party in delivering what is expected or promised. However competence is secondary because failure in competence is more easily forgiven than failure due to lack of honesty and benevolence. Everybody believes that honesty is very important for trust; however the question is what comes first.
Let me use the corollary of a house to explain how relationships are formed. A complete stranger would not be allowed even inside the main gate of the house and would have to yell from outside to be heard. There is a well defined and known protocol for treating guests and based on how much one trust a person, he/she would be allowed access to the front gate, porch, living/drawing room, kitchen, bedroom etc. A stranger cannot walk into the bedroom without being labeled as an intruder and similarly the host cannot welcome a stranger to the bedroom without raising suspicion about the sly intentions of the rendezvous.
In a relationship one has to pass a serious of hurdles before being trusted and unless there is trust, one is scared of telling the truth and revealing oneself. Even if you visit a hospital and ask strangers “How are you doing?” chances are that the response would be “I am fine.”
Everybody is economical with truth and honesty often makes one feel naked and vulnerable. Hence we create secrets and sharing secrets is a way through which a lot of people (esp. girls and kids) communicate to others that they are trusted and also check their trustworthiness. Hence my assertion that contrary to popular perception one has to build up trust before they can expect honesty in most relationships. However once the trust gets build up, there is no faster and irreversible way of breaking it than dishonesty with malicious intention.
On a lighter note, I have known couples who have problems telling their spouses that they are fat or what they truly feel about the new home décor. In most cases, their spouses know the real answer/feelings of their partner and this white lie does not bother them or damage their relationship because the intention was not malicious.
PS: I have had no formal education in sociology.