Elliebee,
I keep coming back to your post because it really bothers me. I think seeing through your post what my wife went through is it. I will give you some pointers that I hope will help you.
1. A compulsive liars first line of defense is deny, deny, deny ( even when confronted with hard evidence)
2. Second and third in either order is usually anger at the accuser or the silent treatment ( the manufactured anger is meant to get you frustrated so you stop asking questions, the silent treatment gives us time to spin another web of lies).
3. Make the accuser feel like they misheard us or never told us what they are saying (gaslighting, it's meant to confuse the accuser, make them think they are the ones with the problem).
4. When finally admitting we lied and will fix the problem, do as little work as possible until the heat is off then go right back to the way we were.
Tips for you or any other person in your position.
1. You have got to be strong (or the liar will just devour you, remember, we usually have years of experience at lying).
2. You will need someone to keep you grounded, someone you can confide in that will support you.
(again, the liar will try to make YOU the crazy one).
3. You need to push the issue ( don't let his tactics distract you) you may need to take a break in the conversation but don't drop it. Get details!!!! It is much easier to lie being vague.
4. The liar needs to have a reason to change(I can't stress this enough) DO NOT MAKE THIS A REWARD! THIS HAS TO BE A CONSEQUNCE! (I can't stress this enough either)
5. Don't take them at their word that they are fixing the problem. Actions speak louder then words.
6. Don't do the work for them, if they are serious they will find sites like this one and be active on it. No matter how much you push, if they are not ready they WILL NOT CHANGE!
This is in no way a comprehensive list but I think it's a starting point. Just remember, we usually have years of experience at this so be prepared for a fight.
This is by no means an easy or fast thing to fix, there will be bumps in the road, be ready to deal with them. If the liar IS working on it and they slip, don't explode on them, just point out the lie. Don't get to high or low with emotion. Good Luck