It's easy to want to add just one more reply, but as you probably agree having a short 100% good exchange beats easily one that ends on a lower note.
Don't stress over how it finished. Just be mindful next time to not try to prolong it.
Plus there are hundreds of reasons not to do with you that texting replies died down quickly. 1. Problem with his phone. 2. Lost signal. 3. Got tired. 4. Headache. 5 match on TV. 6. Talking to you inspired a great Christmas present for you and he had to go get it immediately
Etc etc. Maybe it is none of the above but there are reasons other than shutting you out. And even if he did want to stop chatting with you there are umpteen reasons too.
Don't assume the worst. But do leave it up to him to dictate this.
And maybe he is giving you what you asked for before going dark. It is possible.If so that is great, BUT he maybe still unsure. So absolutely no pressure is key.
Best wishes
R 25 years M 14 years S11 & S13 Working on it alone since Oct 2014 M in trouble a lot earlier (~2 years) Feb 2016. 1st R chat in a yr. Next R chat Aug'17 Still together