Do not make someone discover your withdrawal through repeated unanswered messages.

Pulling away in silence looks passive from the inside and lands as something much harsher. Each unanswered message asks the other person to keep guessing: whether you are busy, whether something happened, whether they did something wrong, and they usually settle on the last of those. Silence is not neutral, because they have to invent the reason.

If you have gone quiet on someone, send a short, plain message this week without a full account of why. Say you are not able to be much in touch at the moment. It is a smaller thing to write than to keep avoiding.