Was it a little white lie? Something that started small and then snowballed? It could even be a great, big untruth told right in the beginning. If you are keeping something from your romantic partner, you should also be wondering how best to confess. Confession is the best thing. For just dating, you have to evaluate where the relationship is going, unless you plan to see this person on and off long term. Any long term relationship should be supported on a firm foundation of trust. If you hold something from your partner, not only are you breaching trust, but you will probably suffer from feelings of guilt and paranoia due to your wondering what your partner might be keeping from you. If you’re worried about this affecting the relationship, admit to yourself that it already is. It’s affecting you, and you won’t be able to fully commit or enjoy yourself with the guilt hanging over your head. Realize that you owe it to the person to reveal the truth. Then take steps to alleviate the mistake you made when you lied to them. Most people believe that they will be rejected straight off; but in fact, if you are honest and give a sincere apology, oftentimes people will be surprisingly forgiving, though perhaps not right away.
First, is it just one misconception that you have to clear up? If not, pace yourself; or pick the ones that are the most major discrepancies (http://www.wikihow.com/Confess-to-Lying). Try to find a private place where you can talk to the person one-on-one. You don’t have to let on if you don’t want to, that you are going to admit that you’ve been lying. You should find a time when the person is calm and not stressed out. Keep your apology clear and concise. Make sure what happened is absolutely clear, that you are sorry, and that it won’t happen again. Also, talk about what you will do to make amends. Explain why you lied. If it was to save the person’s feelings, unless there are other negative aspects attached to the lie, usually the person will forgive you quickly. Some people feel that they are ready then suddenly back out. If you keep putting off the inevitable, the problem will only get worse for you. Do it sooner rather than later, otherwise you risk the chance of your partner finding out on their own. That would be a much worse situation for you. After confessing, ask if they forgive you. Give them time if they need it. Let them know you are there in case they have any more questions. Then try to find what you can do to make up for this transgression. Before you know it, everything will be fine again.