Do not text every day when you're apart.
Your texts should be predominantly to arrange the next meeting.
Do not send "How are you?" type texts.
Never ask him to text you more.
It's fine if you give him the impression that you're too busy with your life outside of him to text him every day.
If you're doing A levels too, try to avoid getting sucked into spending too much of your time or mental capacity on him.
Treat your A levels as a full time job that you're passionate about in which you do loads of overtime (especially in the run up to exams).
When you're on dates with him, have a great time. It's fine if your next date is a lot shorter than 6 hours. And if you cut off the date to get on with something else in your life, such as homework or getting to sleep at your usual time.
As a general principle, the less needy / clingy / desperate person in a couple will be the one that has more attraction power.
And coming over as needy / clingy / desperate reduces the interest and attraction of the other person.