I need your help with my bf

So I saw on my bfs phone that he was messaging this girl. Him and I are pretty open about who texts us. I had asked him who she was and he said, idk. I said, well you do if you texted her. He then continued to not answer. So I put it aside because I didn’t wanna start an argument. He was still sitting by me and I saw that he wanted to unadd her, but instead of unadding her it looked like he pressed the clear conversation button. So I asked again. He said idk when people text me I ask who it is or how they know me. Which he has done before.

Just found it shady when he cleared the conversation, if that’s what he did. He recently changed his passcode too, saying it was because he forgot his passcode. Which is was the easiest one ever. You cannot forget the year you were born. So I’m kinda thinking stuff is going on.

Should I just be honest and ask what is up? Or should I just leave it alone! Please someone tell me what to do!