Another chick likes my partner 😒

Rheanna

So my SO and I have been together for five years this year. Last year we split up for 3 months and got back together. We are stronger then ever now. We didn’t cheat or anything like that. My SO has this best friend and he has a girlfriend. The girlfriend always flirted with him and spoke to him in a way I always thought was a little inappropriate and when we broke up she was there for him even more. He thinks I’m paranoid and that she has no feelings for my SO but I see how she acts around him. I trust my partner. I don’t trust her. Am I being paranoid? Or do I have something to worry about? 😒