jealousy is real bad with the ex

basically my girlfriend still talks to her ex and hes a fuck boy and he keeps flirting with her but apparently they’re just friends and ive been trusting her for ages but they were together for a long time and they know each other very well, she talks to him everyday and keeps saying he’s just a flirty person but it’s makes me so angry and i get so annoyed because it’s like if she has me why would she need to still talk to him? and btw she hasn’t even told him she’s taken yet and she hasn’t told anyone it’s like she doesn’t want to be tied down by me