Friend and boyfriend flirting?????

My bestfriend from college, my boyfriend of 3 years, and I are all quarantining together. We all went to school together so we’ve known each other for quite a long time and my boyfriend has always been like a brother to my friends. Or so I thought?

So when covid hit we have plenty of space so my bestie moved in and everything was cool. Like I said we all know each other so I didnt feel like I have to monitor them or be awkward or anything because we’re all friends. But over the last month or so they’ve been acting weird, texting each other (I didn’t go thru his phone but I’ll glance see her name in his messages if we’re next to each other), and on numerous occasions I’ve walked in the room and they stop talking or switch subjects

I haven’t officially mentioned it or anything BUT I even asked him what they were talking about and he told me to ask her so i did, and she told me to ask him and he didnt tell me!!! So ive been feeling very weird lately and I dont know what I should do but I’m definitely not staying in a situation where I’m being played like a fool.....