First thing that entered my mind was that you texted him that you wanted to be friendly. I'm not sure what your intentions were about that, whether you were saying "just friends" or not by how you worded it. The thing that I think might have happened is that maybe because you had sex he thought it could be more and is feeling rejected?

Now I'm not here to try and make you feel worse. I only mention this so that maybe you can find a solution. If that is the case, that he is feeling rejected, personally maybe he needs to understand a bit more about how you feel about things. Obviously not too much because you've said he's not a close friend at this point but I think that somehow making him understand you better is key.

I think he should at least reply but I'm just giving you my 2c about what might be going on.

Try not to feel guilty, it was consensual so nothing wrong with it.