Need Help/Advice

I was looking at my boyfriends phone and came across this. The number wasnt saved in his contacts so I'm not sure who it is. I asked him about it and he immediately got defensive. I said that I was just wondering what it was about... It was from Friday and I saw it Saturday and ask him about it Saturday. He says he doesnt know who it is and that he didn't send the message. He said it could've been his co-worker that needed to use his phone. I dont believe him, this is how he writes his texts so I find it hard to believe that it wasnt him, its on his phone... I cant stop thinking about it, here it is 11pm and I cant sleep bc it's on my mind. Im not sure what this means and Im hoping someone might? I was not home during this time, he gets out of work before me. I don't like feeling like Im being lied to.. I need some help/advice please!