Should I be worried

I 26F am with 29M. So I found out that he was keeping in contact with an old female which he had a sexual relationship with for about 3 years on and off. I recently added her on social media and sees that she constantly looks at all my stories. When I go through my bfs phone i see that she looks at all of his things too and sends him messages. She lives in a state in which he will be traveling too in the near future for a work meeting. In the past( before me ) whenever he went there for family or work purposes , he has met up with her .. should I be worried ? He says that everything is fine and that he is not in to her anymore ..