If he can't respond to a text msg, he may not be talking to you in person. I don' t know his boundaries, he would feel confronted if you texted him by phone when to talk to him by phone. Crossing the boundary of sex may have meant that it's difficult to figure out whether the friendship is difficult to continue or something has caused his behaviour.

Hope you get more feedback from others here at PC. This post is just a suggestion- take what you like and leave the rest behind.