The truth of the matter is that if someone is going to cheat you simply cannot build a wall tall enough to keep them in. One way or another they are going to find a way to do it.
As hard as it is to hear, the only real solution to this type of situation is to ask yourself if you can trust this person or not. If the answer is no, then you’ve got to ask yourself this next question: why would you want to be with someone you can’t trust?
I am a firm believer that you cannot expect someone — anyone — to show any more respect for you than you show for yourself. If you don’t trust this guy because of his lies and dishonest behavior, then you need to demonstrate that the behavior is unacceptable to you and that you deserve better in the only way that matters… by giving yourself the opportunity to meet and date someone you can trust.