Is he cheating if he is deleting his text messages?

A couple of weeks ago my long-term boyfriend and I were hanging out. He started receiving text messages. They sent several messages back and forth. Each text he received he would smile or chuckle. I wanted to know who he was speaking too so I checked when he left the room. He had erased his entire inbox and outbox. This isn't the first time this has happened. Once, I checked his phone after a similar situation. He had forgotten to erase the outbox. He was texting a woman he used to have feelings for before we starting dating. They were arranging plans to meet up. I spoke to him about this later and he told me that the plans fell through so he didn't think it was important to tell me. After these words, I let it go but I am obviously still having trust issues. Am I being suspicious over nothing? Should I speak to him again? Or should I just butt out?