Do you find that he’s generally not a great communicator? Have you noticed this type of thing in his other relationships? Were there signs? Has he been acting different/ distancing himself from you, that you’ve noticed?
It’s hard to say what’s going on because he’s not telling you. I’ve been in this situation before too (there were drugs involved, but I saw it as the person- immaturity and lack of communication skills and things being a mess all around). It’s a horrible feeling. In my opinion doing “no contact” is done for specific reasons, and/ or when previous efforts to communicate failed, and the perhaps the situation became dangerous/ chaotic and it’s fight or flight- not something that you do so you can just stonewall people and have them have no idea what you think they did wrong (if that’s the case), or where you think things went wrong. But never the less, this is what he decided to do. Maybe that’s how he breaks up with people- something goes on in his own head that he doesn’t communicate, then he makes the decision to break up, and he goes silent?