How should I [M 23] react when my gf [F 23] bring up the topic of her ex?

Okay so i [M 23] know this is a very common thing to happen but I still want to know other people’s opinion on this matter. So recently, about 3 months ago I matched with a girl[F 23] on hinge and ik what people say about online dating but this girl really does feel special. We have so much in common, we vibe a lot and we understand each other. We talk almost all day and she does mention her ex [M 23] a lot. Now she had recently got out of her relationship of 1.5 years and we started dating in less than a month after her breakup. Now they work in the same company so it is inevitable for them to not meet but she does mention him a lot. Now she does like me a lot i can feel that but there is a constant fear in my head what if he convinces her to get back because of the history that they have. They are still in contact and she does bitch about him a lot. Now ofc i wont tell her to stop talking to her ex so how should i react when she brings him up the next time