He stopped writing good morning texts. Does it matter?

The morning message was a ritual, and its absence can matter because the ritual mattered to you. It does not by itself establish that affection has gone. The rest of your contact may have changed too, or only this habit.

Naming what you liked about it is more precise than asking whether he still cares on the basis of one missing text. The conversation can make room for a different ritual that suits both of you.