Boyfriend getting too close to my friend—am I overreacting or is this a red flag?

My boyfriend and I recently started dating near January of this year, we were friends for 3 years before this and both have been in multiple different relationships. He’s genuinely always been extremely attentive to me and always there for me, and now our relationship is the best I’ve ever had. But lately we have been arguing a little more and this all started around when I introduced him to a girl I had class with and have hung out a few times. He’s extremely nice to everyone and an incredible conversationalist, and also always had more friendships with girls, so I didn’t think there would be an issue. However, for
the last month or so they have their lunch break together everyday and have gotten to know each other pretty well ( him buying her things, shared Spotify playlist, inside jokes, seeming more comfortable around each other, and always smiling at each other ). I don’t want this to bother me, but she’s been hanging out with me and him the majority of times him and I get to see each other in our busy schedules.

I brought this up the other day to him and how it made me feel uncomfortable, and he agreed and decided to try to see if she liked in any way and distance himself. The next time we all hung out with each other she looks at me like I told her I ruined her life. He told her about everything I said. They started ganging up on me and that “ it’s a personal problem” and that they should be able to have their friendship. He started to raise his voice and began saying things like “ she’s the only person who makes me feel okay right now”, and things like that directed at me.

We sort of worked things out but I’m more upset that they have a stronger emotional connection and that he’s somewhat seeing her side more than mine. How should I approach this? What do I say? Should I take a step back?
Boyfriend getting too close to my friend—am I overreacting or is this a red flag?
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