Now we have the actual story of that she also didn't text for 3 days. I reckon that he was wondering whether she is actually in to him and wanted to see if she would even initiate the conversation. If after three months a girl I was seeing still wouldn't text me first I would probably dump her.
She does and has contacted him first, and that is now more often than not how the contact goes. So from fairly even from both party, to her being the main initiator of contact, which obviously make her worried and also doesn't want to seem like she is being clingy, so when she doesn't contact, he doesn't either.
Damned either way.

To re-iterate, if this is how he had always been, no problem, but it is instead a somewhat large shift in behaviour in just a few weeks. From making plans to see her multiple times a week and daily contact, to this.