OP, you are getting a very hard time on here. AIBU can be a bit brutal. You might want to go to the Relationships board.
I think you should not meet the other man (for now) and have a long hard think about what you want out of life.
Forget about the other man for a moment.
If you are unhappy in your marriage then you should end it and give your husband the chance to meet someone who will love him. Presumably he doesn't know what happened all that time ago and if he is a good man he deserves that chance. It isn't his fault that you made that decision. You might only be yearning for the other person because you are actually just unhappy. It doesn't mean you don't love your husband, you can love someone but not want to be with them.
You shouldn't have to do what is expected of you. I find it very hard to understand the religious mindset that makes doing the right thing according to expectations rather than what makes you happy (providing you aren't hurting anyone or doing something illegal) the most important thing in life.
However you chose to stay with your family and your community for reasons 12 years ago. Are those reasons no longer important to you?
You have children to consider. If you are unhappy they will pick up on that. I personally think it's better for kids to grow up with happy parents. But you will be turning their lives upside down. So you have to be sure.
You also have to think about the other people in this situation besides your children and husband. The other man is not treating his fiancee well by having an emotional affair with you.
If you want to be with him then you both have to end your current relationships before you start anything. You would be making a big sacrifice for him in terms of the effect on your kids, hurting your husband and family cutting you off. It could work out. It could be incredibly hard and the relationship might not cope. It's a lot of pressure to put on someone.
If he really loves you he will agree and wait for you until you are ready.
Could you speak to a counsellor about how you are feeling? Sometimes talking to someone impartial can help things seem clearer.
I'm sorry you are in such a messy situation.
I can't believe the word cuckold has actually been used in this thread.
I wish you luck OP and I hope things become clearer.