the answer may well be yes, you should leave, but there are definitely issues with this.
First, are you sure it's not your gf's unattainability that's making her seem wonderful? Living with her for a month is a good start, but are you sure there won't be rows about leaving the toilet seat up and whose turn it is to put out the rubbish? Because if there's any friction it will be compounded your wondering whether you did the right thing, and remembering how things were different during your marriage.
And there's your wife. She's given you most of her life, as well as providing you with children. Now you've found something better. But her life is going to be dreadful. Since you married her without loving her, it's your job to make this as painless as humanly possible - and it's never painless. It seems pretty clear from your post that you've decided to go and you want people to tell you you're doing the right thing. You are - for yourself. But you're going to devastate the lives of your family (kids too), possibly forever. Up to you to make this work.