Thanks for writing to Just Answer.
Obviously no one can know whether you should leave or not except you. What I can do is give you some things to consider as you make this decision:
1. Your relationship with your children will change. You will become an onlooker to their lives, rather than a full participant. Spending weekends with them, and trying to also keep your girlfriend happy will be a challenge. Children rarely get on with the person who broke up their parent's marriage. They will feel a loyalty to their mother, most likely, and that will create a strain.
2. You will have financial challenges. Even if you have both been unhappy for years, your wife may fight very hard for financial support, especially for the children's support. Do you make enough to essentially support two households?
3. Often, even though a man has left his family for a woman, she will have jealousy over the time, money and energy he spends on his children and helping the ex-wife during the crisis's that will inevitable arise over time.
4. If there will be a financial strain paying child support and setting up a new home, that will take the glow off the new relationship faster than anything else. She may resent that a part of your income goes to support your children. I know when you're first in love that seems impossible, but my years as a counselor and my experience answering questions here, I can assure you it's a common issue.
5. Your new girlfriend knows you are capable of cheating...because you did to be with her. After the first year or so, you may have to deal with her rising suspicions about where you are and who you're with. You would be surprised how many "new wives" write in to us about that.
6. Have you thrown yourself, heart & soul, into making your marriage better? Do you have a clear conscience that you did everything possible to try to make it work? Have you gone to marriage counseling and truly participated?
I think if you fully think out the issues above, you will have the information you need to make a reasonable decision. I focused on the negatives, as you already know the positives--being with the new woman, and feeling the excitement of a new romance.
This is a difficult decision you're faced with, and one that will have life-changing consequences for several people, including your children. You might want to meet with a counselor for a few sessions to think this out with a neutral third party. Too many people make this decision in haste, and it's too important to rush.
I wish you the best as you make this difficult decision,