Relationships are built on trust, and loyalty. A key component of both of those things is honesty. To trust someone, they have to show their honesty to you, and in turn you reciprocate. The same goes for loyalty. For one to be loyal to someone, there has to be a commonality, even thieves can be loyal to one another, but they have to be honest in their "honor among thieves" with one another.
The context of the relationship doesn't matter, but this point holds true regardless...if you are honest with each other, both parties are much more open to making the partnership work. Honesty doesn't allow for unconscionable contracts in business dealings. Honesty doesn't allow for mistresses on the side in marriages. Honesty doesn't allow for friends to be talking about a friend behind their back and saying they something different to that same person's face. One of the definitions of honesty is 'freedom from deceit or fraud.' That's honesty in a nutshell. Let's not live our lives with ulterior motives. Let's not try to find ways around tough situations by making them tougher. My pastor said this week, "no one has to tell a child how to lie, they are sinners by nature." We all fall short of the Glory. Knowing this is true, make it a point in your life to work to overcome that shortfall. Simply tell the truth and deal with the consequences. The consequences of being caught in a lie are almost always worse, and even when they are not exposed externally, we have to live with that guilt on our conscious every day. It's simply not worth it. Be open and honest, and people will respect you more than you will believe.