Hi Lex,
He may have started acting weird because you didn’t turn out to be what he was hoping for.
He may have initially showed a lot more effort in trying to get to know you because he already had preconceived notions about the kind of person you were and that may have drawn him to you.
However, as the both of you texted each other, he may have come to realize that you don’t match the kind of person that he was hoping for.
Hence, he started replying with shorter messages and has now ignored your last text message entirely.