Am I overthinking or is there something going on?

I’ve been dating this guy for over a year now. We work at the same place and have partners every day. This new girl started towards the end of last year and she’s always been kind of snooty to me. The guy & I share the same locker and I started to realize a few weeks ago she started to put her things in there & leave sticky notes to him. I brought it up & he said it’s harmless. Recently, she’s been picking up shifts with him & I’m not sure if he asks her to or what. I’ll ask him who he’s working with the next day & he’ll usually say he doesn’t know or his normal partner. But then she shows up. Any time they work together he doesn’t text me as much & it does bother me. This girl is actually married, but I’ve heard through a lot of people that she flirts with so many guys. I’ve mentioned to him before that I don’t like her or how she leaves sticky notes but he always promises me that it’s harmless & that she’s married. He’s overly friendly bc that’s just who he is as a person & I wonder if she takes it the wrong way. But idk if this is something I need to bring up again? He hates when I get jealous but he’s gotten jealous before & I know if the roles were reversed he’d be super jealous. Idk what to do bc I don’t want to start something that I may be overreacting to.