Thank you for your question. Right now your emotions are torn on who you want to choose.
You do have to make a choice.
It sounds like you are leaning towards being with your first serious boyfriend more than your fiance.
You mentioned at there is a lot of damage done in your current relationship that you feel can not be repaired. I feel the reason why you cheated was because you were looking for an escape to get away from your current relationship.
When two people first start dating you are out to impress the person and things are new and exciting. You learn about the person and things start off good. As the relationship progresses things get more comfortable and then things get into a routine.
If you want to work things out with your current relationship you both would have to find the reason you both got together and how you both felt when you both decided to make that commitment to the future to get married.
Right now I feel your feelings are blocked for your fiancé because things have happened that effected your feelings for him.
He is the father of your children and you will always have a bond together.
You want to be fully sure when you make the decision to move on. I want you to think about what is best for you and what you feel you need when it comes to this relationship.
You are asking him for a break, but I want you to be sure how you feel.
Some times when people break up and try to move on with someone else they realize that they want to be with the one they left. Even if you want to move on, you still will feel the effects of a break up.
There will be things you miss and your feelings will get confusing on how you feel.
I want you to take the time and really think about how you feel about both of them and who you can see yourself not being able to live without.
You mentioned you love them both and that is understandable, they both have certain qualities that you love.
Also if your fiance finds out you cheated you want to think about how you feel he would act and if it is something that would put a huge strain on the relationship.
This is what I want you to do. When you wake up tomorrow mourning think about who is the one person that if they left your life for good.
Which one could you see yourself not being able to live without.
This helps in discovering your emotions.
You might not know right away who you want to be with, but I do feel that so much has happened with your current relationship that it has effected how you feel about him.