I know it's hard when you love someone, to imagine your life without him or her. I have a couple of suggestions on how I evaluate things. Maybe they will help you make a decision.
I ask myself one question on determining if someone should stay a part of my life:
1.) Is my life better with this person in it than without?
If my life is better with them, then they stay. If my life is not better, then it's time to break all ties.
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Another decision making tool is the 10-10-10 (from Oprah).
Ask yourself: How is this decision going to affect me in 10 minutes?
How is this decision going to affect me in 10 months?
How is this decision going to affect me in 10 years?
If you leave him:
.....in 10 minutes you will be in shock and tears.
.....in 10 months you will be divorced and have moved on with your life, out of limbo and LIE free.
.....in 10 years you will be married to someone who loves you, who doesn't lie and have a beautiful stable family.
If you stay with him:
....in 10 minutes you will be the same, exhausted, wondering if will ever stop lying.
.....in 10 months you will be in therapy and he may or may not be lying.
.....in 10 years he may still be therapy (depending upon his illness), may or may not be lying. If you have kids and he's still lying, you will be miserable and your kids will be suffering. If he isn't lying, you will hopefully be happy and thankful and be great parents.
That's an example of how the 10-10-10 works. You have to answer those questions yourself.
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Other people are suggesting counseling and that is not a bad suggestion as long as you are realistic of the positive and negative outcomes and the amount of time you have invest. If you feel you love him that much to devote the time and energy AND you truly think he wants to change, then stay. Help him. We all need to help make this world a better place and by making it a better place, we need to help make those who live in it better people, including ourselves.
If you choose that route (therapy), you have to be prepared that you are going to invest years of your life with this man while he is in therapy trying to correct this problem that may never be fixed. And he may need to be in therapy forever. I know someone who’s been in therapy for 25 years, is still going and still not better.
However, if he is not aware of his problem and your gut is telling you he really doesn't want to change and he's not remorseful, then leave. My gut has always been right (even when I didn't want it to be). Someone who lies that much has a psychological problem and is not going to stop lying on his or her own or for another person. I have known multiple people like him over the years. They lie about things that don't even matter----so why do it? I've had 4 co-workers, 5 previous friends and have one brother who is like that. And my experience is there is no changing.
At this time, DO NOT HAVE KIDS with this man. Do not have kids until you both are stable and ready to give 100% to your children. You can't support him through therapy and take care of the kids by yourself. That would not be fair to you or the kids. Plus raising kids is a two-person job, he needs to be able to take care of the kids too and teach them good morals and values. If he lies all the time, what kind of example is he setting? Our children are little versions of ourselves and are usually a direct reflection of our parenting. We are responsible for the kind of persons our children turn out to be. "Handle with care" label should be on all children at birth. You do not want to start a family with this man not knowing if he is going to be there in a few years or be of any worth as a father.
I don't mean to be harsh. I have just been there, done that. I wasted years and years on worthless people who never really cared. You just have to know when to get out and when you stick around. Some people can change but it's very very hard and they usually have to hit rock bottom before doing so, if ever.
I wish you wisdom. I wish you courage. I wish you strength.