What’s the best way to come to terms with the feeling of betrayal if you’ve already talked it out with the person and still feel the same?

There will be no feeling of closure if that is what you are hoping for. What I’m gonna say is basic advice, but it’s realistic. You can dwell on the betrayal but it will not do anything good for you if you let it consume you. All you can do is move on, forgive, but do not forget. And forgiveness is not always about forgiving the other person but rather yourself, for trusting them.