Girl ‘friend’

I need advice okay so my fiancée has this friend who’s he’s been friends with for 2/3 years and when he first got together they weren’t as close and he told me how when they were drunk the had sex and it was a one time thing etc and now all of a sudden she’s back and they are getting vvv close again, I don’t mind him having friends that are girls but for some reason this one girl is really really bothering me, he sees her once sometimes twice a day and it’s really bothering me.

He also refuses to let me near his phone

Am I being crazy or do I have the right to feel annoyed