A lie to another lie

Today I found out his seeing someone. He never admit to me again. How am I going to be honest to you if you have been never honest to me from the start we are together until now. I have been honest to you from the start, but my honesty will be lesser each time you lied. How can I be honest to you when you aren't to me. You know whatever you do I will forgive you but you choose not to tell me. I can be honest to you if you will start to be honest to me now.