Hi! I believe I can be of help with this issue. First, let me say I can imagine how frustrating this situation must be for you. You are a well-adjusted young man in a good relationship but you have this one "habit" that is so problematic and embarrassing to you. And I'm of course talking about the lying and not the cigarettes!
What's fascinating is that in my private practice I am seeing right now a man in his 40s who has come to therapy for this exact reason. Not lying about smoking. It is more pervasive for him. His wife will ask him about almost any little thing, like did he do this or that, and he will lie and say yes, even though she will find out and if he hadn't lied, she wouldn't have cared anyways. He could have just said he'll do it later. We've been working on it for a little while. And then he also makes up stories to inflate himself socially when he's talking with people. And then his wife will hear from someone about her husband doing this or that and she knows it's not true. And he's again embarrassed.
And where he's gotten so far is that he was made fun of very much as a kid. No abuse, normal family, but a lot of anguish at being made fun of. By a few kids throughout his schooling. And he still feels those feelings inside of having to be important or not criticized, etc.
Now your situation doesn't sound as severe and you may be able to deal with this on your own. Looking into your feelings when you lie, what actually happens to you in your body may help you get more to the source. And that is always helpful. But you still need to take some remedial action. Here's a technique that may help you quickly deal with this:
Practice every time your girlfriend asks you about smoking taking a deep breath and not answering. The idea is you are trying to break the lock in your emotions that happens when she asks and you freeze. And then you lie as a reaction to this emotional lock. So practice taking a breath first and waiting. Wait until you have an active, conscious thought. A thought where you can say, okay, it's me. What is the answer? Say the answer to yourself. Then say the answer to her.
You might want to show my answer to her so she can help you with this. This will be a great technique for you to help you with this. Because you clearly go into a locked emotional state where you answer quickly and then find yourself having blown it again. So break that lock.
I wish you the very best!
Please remember to click the green accept button. Feel free to continue the discussion; my goal is to get you the best answers possible. Bonuses are always appreciated! If I can be of further help with any issue, just put "for Dr. Mark" in the front of your new question, and I'll be the one to answer it. All the best, XXXXX XXXXX