he thinks I cheated

So the other night I was laying in bed with my boyfriend watching Netflix on my phone  when this guy that is only a friend and nothing but, texted me and said "hope you had a good day, love yah" like he does every once in a while. This is a guy that is very very depressed because he has no friends and thinks he's going to die alone. I have made it more than clear that we are just friends and he knows that we are just friends. But my boyfriend doesn't see it that way. He completely flipped out and he is convinced that I cheated on him. Granted, there were no other messages between us on my phone and my boyfriend is out of town a lot so I can see why he thinks this. My friend sent screenshots of the messages to my phone so my boyfriend could see them and he's still convinced I cheated. I literally have no idea what to do. I know what cheating is. I know that having a friend that is a guy and is just a friend, is not cheating. This happened in the middle of the night on Monday, it's now Wednesday and he's just now starting to talk to me. But when we do talk it's questions regarding my friend and every detail of our friendship and he talks like I cheated. We had sex earlier but it was the most meaningless and emotionless sex we've ever had. He accuses me of cheating when I know I didn't. We've been together for 3 years. The friend is aware of that and asks me how me and my boyfriend are doing whenever we talk. Me and my boyfriend have been through hell and back with eachother and I honestly don't know if our relationship can survive this. I didn't do anything wrong. Or did I?