A friend of mine attended my birthday few months ago and she met my other friend which happens to be my best friend. Now they are both close, my best friend even goes to her house to visit her. I really don’t feel good about it cause she’s my friend, why is my best friend getting so close to her to the extent of even going to her house to visit her. I don’t know if I should address it or just let it slide. I know some friends through best friend too but I don’t get too close to them.