Oh, I have been there and done that! Time and again. I wish that there was no option to see whether or not the other person has read your message. That would eliminate SO much stress. I wish that it were set to where the only way to know if they read it is if you are seeing the three dots in motion, meaning that they are typing a reply. And it is stressful. Especially if you think like I do. The first thing I do is say "oh, that's it, so and so hates me now. Even though I can not think of one single thing that I could have possibly done to make so and so hate me, I know I have done something. I just know it. That's it, I have destroyed a great friendship. I didn't just burn that bridge, I NUKED it!!". Then, I hand wring and worry something fierce. I will say that it does help me to look at it another way. If the person who is not responding to me really wanted nothing more to do with me, then they would just unfriend and block me, and in fact, probably would have already done it by now. So, that helps to calm my worries some. Not a lot, but some. Basically, what I do is just try again the next day. And what's funny is, nine times out of ten, the next day they actually do reply! And then I breathe this huge sigh of relief. One time I decided to ask someone about this. I said "just curious, was everything alright the other day? I messaged you but didn't hear back, so I was just hoping you were okay." While their answer was very vague, at least it told me something. They said "oh, yeah, everything is fine. Don't worry, my not replying didn't have anything to do with you." I took that to mean that they didn't reply to anyone else that day either. Or, at least I hope that was what it meant. Anyway, it sucks to the nth degree nonetheless. But, when this happens again, try to think of it in terms of if they were really mad at you, then you would have been unfriended by now. And then message them again a day or so later. Hope this helps!