What would you do?

So here's the back story, me and my boyfriend have been together for a year and 6 months now, and I can honestly say I love him and trust him completely. There's this "friend" let's call her J. J was new to our university and I helped her get settled and everything. We became friends and i used to always check up on her and everything. Well after a couple of months she started acting weird (I.e. Not talk as much whenever we were together and/or leaving soon) I never thought much of it because I was busy with school and work. 
One afternoon I was getting ready for class and my bf asked if I wanted him to bring me lunch and I said no because I wasn't hungry, half an hour later he showed up with food for the both of them. Keep in mind, that they were never friends but used to say hi and stuff because we used to hang out together. So this intrigued me, the next night I was at her room hanging out with her roommate (we are very close) and my boyfriend was sitting next to me, so I had to borrow his phone because I left mine home and a message from my "friend" pops up. She was sitting on the other side of the couch and instead of speaking out loud she decided to text him. When I asked my bf, he just told me she usually does that sometimes. He then showed me their msgs, and she was pretty much flirting with him and asking him to take her to the gym and show her some "moves". And my poor bf 😂 told her to contact a trainer because he didn't have time. He never realized that she wanted Him and that she was trying to Flirt...
I cutted off all contacts with her, but I wanted to see what you guys think... was she being sneaky or was I over acted?