Sometimes secrets are like sores on top of our skin, swelling increasingly with every moment just waiting to pop. We have to relieve the pressure at some point or the pressure will be relieved on its own. We may think that secrets are necessary, but there is nothing like the freedom of being truthful. Not only does it ease the stress on your mind, but it will provide for an open clean slate in a relationship. Have something on your chest that you need to get off?
It is important to start by comforting the person whom you are going to reveal the secret to. Let that person know how much that you care for them, and that you are telling them this secret in order to better your future with them (which I am assuming you are). Then proceed with telling them what you need to tell them, make sure they hear everything without interrupting and if your secret evokes an emotional response, do not try to defend your reasoning for keeping the secret, remember you were the one who wasn't being honest. After you discuss the secret it is important for the both of you to evaluate your future together, make sure the person you told the secret to is willing to move past it, this may require time, but it is essential to look towards the future. If your relationship can not move on because of the secret that you told it is important to cut your losses, and move on without each other.