Honesty is the best policy as it is a sign of human integrity and being a good person.
Honesty is the strength binding all relationships; friends, family or partner. By being honest you have a clear conscience and you are respecting the person closest to you. Honesty is a step to free yourself from any fraud, deception or the smallest of things, like taking something that you shouldn't have and owning up to it.
No matter the severity of whats being said, by being honest it might worsen the situation or make you feel vulnerable yet, it's important that you are being true to yourself. As a result you've lifted a burden off your shoulders and now the ealing process can begin.
Yes, there comes a time in our relationships where you might feel that by keeping something away, your protecting the one you care for. In all fairness, you don't want to hurt the one you care about therefore, you keep it to yourself but reality is, that your only making the situation worse.
It's important to be sincere and truthful in all relationships because, that's what makes a strong and ever-lasting bond and builds good character.