Telling the truth, or we can say honest, is very important to all kinds of relationship. As people always say, truth is like a piece of people, when you ruin it, it will never become the same as before. Moreover, truth is the base of all the relationship, how could you interact with a person you cannot trust? Therefore I think truth is the most important factor in all kind of relationship.
First of all, not telling the truth, which is lying, can leads to more lie, and eventually leads to the ends. For instance, when ones girlfriend ask her boyfriend to go out, but the boy doesn't want to go because he got a party to go. Therefore, the boy lie to the girl saying that he is feeling sick, instead of telling the truth, because he don't want to make her girlfriend unhappy. This lie might helped the boy to make her girlfriend happy while at the same time, he can have fun in the party all in short term. But in long term when the girl find out the boy is lying, the girl will be very angry and sad, which means the relationship might face a end. From here, we can know that lying at the first place might be fine, but never work in long term in any relationship.
Secondly, not telling the truth in long term will makes people stop trusting you. And when this occur, that person will be very sad, and hard to find stable or real relationship. For example, one of my friends he always lie to us, at first we believe him. But after we knew he was lying, we just stop playing with him. And once, he was even telling the truth, we still did not trust him. Therefore, we can see that not telling the truth will make you have bad relationship you're your friends.
In conclusion, telling the truth is the most important part in any relationship, because a relationship without trust will not last long. Even though some people might aruge that other consideration such as love, communication is important in any relationship. It is true, but how can you communicate or love a person that...