What I got from your post is that this is your first romantic relationship outside of your marriage. You haven't dated since you were a teen (I've been with my husband since I was 17, so I know how it is). Take your time with this relationship, have the serious discussions, see if the 2 of you really are a good match for each other on a deeper level. Is there a possibility that 10 years into a mono relationship with Bree and 2 kids with her that you're going to feel the need to "sow your wild oats" again? You would hurt her a lot worse down the line than you would now by honestly looking at things and saying that long term the 2 of you aren't compatible on a basic level.
I would also like to echo what other people have said. This is a brand new relationship and as such you shouldn't be making any life altering decisions yet. Give it at least a year and a half (especially since it's a long distance relationship). Once the NRE of the relationship has worn off you can look at how you really want to have your life structured. Maybe you'll decide that you really do want to be mono in which case it will be time to sit down with your wife and figure out how to transition in such a way that will cause the least damage to your children.
Everything will be ok in the end. If it's not ok it's not the end.