Is this suspicious???

So recently my boyfriend started following this new girl on Instagram. I never saw or heard of her but his business partner was also following her so I didn’t think anything of it. That was like a few weeks ago. Today, we met up for lunch & I had a coupon code on my phone, but since it was dying I texted the code to him. So when he opened up his phone I saw within all the messages a convo with that same girl’s name and the last message one of them sent was 😜. As we sat down to eat I noticed he swiped and deleted a convo. Sure enough it was that one. So I asked “whod you delete a convo with on your phone” & he denied it then said I’m accusing him and got defensive. I was like “no I didn’t say anything I just asked.” & he’s like “no your whole mood went from 10 to 0 and you’re implying I’m cheating or something.” I do have trust issues sometimes because once I saw him complimenting an old acquaintance flirtatiously and got pissed off. He said it’s nothing like that but if it bothers you I won’t do it & I just dropped it because that girl lives in another state. This girl, on the other hand, lives in the same borough as us. Is this sketchy? Should I be concerned? We have been together for almost 4 years. I trust him but idk I found that weird. Also, we don’t post any relationship pics on Instagram because of relatives & family who can’t know for religious reasons so anyone new would assume he is single. Thanks for any advice or simply listening! ❤️