For anyone, the first few months after such a disclosure is just awful, the first couple of years is a trial.
Double betrayals are awful things.
Nothing that you are experiencing is unusual in such circumstances.
having a really hard time getting over what my ex BFF did to me with what seems like no remorse
This person probably has no clue what she has really done, and doesn't have the emotional wherewithal to even begin to understand. If she did, she would not have done this. You can't expect anything from this person.
my fwh, who has really done a lot to help heal our marriage
This is where you can and should expect more from. If, with all the work stress and other family issues, he could find time to have an affair, then he can find time to reassure you, text you, talk with you, go to counseling with you, etc, etc.