Why does he leave me on open and respond later

A read receipt confirms he saw the message. It doesn't confirm he thought about it, wanted to answer, or chose to hold off. People read messages in the car, between tasks, or while half-listening to someone else, and plenty of them mean to come back and then forget. So the real question isn't whether he read it but what the rest of his behaviour looks like. Does he start conversations? Does he sound energetic when he does reply? Does he ask you things back? Those signals tell you far more than the timestamp on one message.

If your messages get read and answered within a day or two with real engagement, the gap is probably logistics. If they get read and then nothing for a week, while he's still active on his phone elsewhere, the gap is about priority. Notice whether his replies, when they come, are long and warm or short and flat. Short and flat plus long delays usually means low interest.

When someone is busy, a message that asks for a paragraph becomes a task they push off. A message that asks one clear, easy question gets answered because it takes ten seconds. So the shape that works is a single thought with one hook at the end, something he can reply to between other things. Skip multi-part questions, and skip anything that makes him think hard about what you meant. Put the context in the message itself so he doesn't have to scroll back to remember what you were talking about.

When you do want a longer exchange, say so and offer a time, or suggest a call. Saying the conversation is worth more than a quick text takes the pressure off him to reply right away, and it gives him a clear next step instead of a vague hope that he'll pick it up.

A reasonable window is about a day for a casual text thread, and a bit longer if things have been slow for a while. If he hasn't replied after that, one gentle follow-up is fine, framed as a light reopener rather than a question about his silence. After that, stop sending. Two unanswered messages in a row is already a clear signal, and a third tends to make you look more invested than he is, which often makes the next reply take even longer.

When he does come back, reply at a normal pace and don't mention the delay unless he does. If he apologises, a simple acknowledgement is enough. If he keeps going quiet over a couple of weeks while you're still the one starting things, that's your answer. Drop the thread and let the next move come from him, or accept that it isn't coming.