He always texted me first, and suddenly stopped. Is he losing interest?

The change is in who starts the conversation. It may matter to you even before you know why it happened. Fewer first messages alone cannot distinguish a changed routine, a different expectation or a change in interest.

What follows your openings is useful context: does he engage, ask about you and help arrange time together? If you want initiation to be shared, the line below names that wish without testing him through a planned silence.