HELLP: Am I just being a crazy girlfriend?

Soo, recently me and my bf got an apartment behind from where he works. We both work for the same company so he convinced me to transfer to the building he works in. I agreed and now we not only live together, but also work together. I love it except for this one chick at work. My first day, people asked who I was in a relationship with, when I revealed who it was, they commented with “oh I thought he was dating (the chick’s name)” Hearing that completely shattered my heart. Like it fucking hurt. I confronted him about it and he reassured me that there was nothing going on with them and that she felt more like a big sister than anything. I cooled down after that but more people kept saying how they thought those two were together because she would drop everything to help him and they would also have lunch and always take their breaks together. Then one day his phone went off and it was her. Like why would he have her contact information? Really? So I got pissed, he told me that it was once again just because they were friends but agreed to delete her. Now at work their jobs require them to work side by side and I get to watch as she continuously flirts with him. He talks to me all the time about having kids and having a life together and I trust him but I surely don’t trust her. Maybe I just being crazy. Maybe I’m just putting my past relationship experiences into this one..

What do you guys think?