Bf asked long time female friend to hangout?

So my boyfriend (we’ll call him Bobby) asked his friend (we’ll call her Betty) to hangout later. He and Betty have been friends since grade 9 a few years before I even knew him. They haven’t talked in a while but I have met her and I like her and she respects our relationship and we follow each other and stuff. They tell each other when stuff is bothering them so they really seem like brother and sister. But there’s always that gut feeling of “why are you asking her to hangout?” Do you think I’m overreacting? If she’s been around this long and nothing has happened, should I not worry?