The thing about girlfriends is: they are a necessity. They know your deepest secrets. They hold you when you're sad, and even when you throw up! You raise your children together, you care for each other, and even if - dare I say it - a close friend betrays you, the reality is that you can't do without them. You may go for a period not trusting anyone and dumping a friend, but you'll throw your heart to another. What does it take to be a good friend?
Loyalty and non-judgemental love are the most key ingredients, particularly in your forties. Why? You don't have time to play games - in this decade of your life. That kind of girly game-playing is for your twenties and younger. By the time you reach your forties, you should have weeded out most of your toxic friends and should have a group you can count on. The time for catfights are gone and unseemly.
Loyalty is one of the most admirable qualities in a person in general. You trust friends with private information, sometimes imtimate. You need to know they will be loyal with whatever the subject is at the time. You need non-judgemental love, as you will receive criticism elsewhere, even from your family. Your friends are the family groups that you set up after leaving home. They take you in and care for you just like family. Their support may save your life one day. It's important to foster the best communication rules about being completely honest with each other from day one.
If you're not honest, loyal, and are full of nothing but criticism, you could lose a friend. Women in their forties don't play that.