It doesn't have to be an all or nothing affair. You can start by telling one truth. If you're in the habit of lying/have trouble telling the truth it can't change all at once and setting yourself up by believing you can "fix" it once and for all will lead to disappointment. Pick one thing you want your T to know and tell that. Not something you think they "should" know but something that it's important to you that they know. Were it me, I'd merely state I had been lying and wanting to change that behavior and discuss why you lie, etc. like you did in this post.