My boyfriend (15) and I (15) love each other very much. He wants to have sex with me. Do I have to have sex with him so that he doesn’t leave me?

It’s great that you both like each other so much.
Now your boyfriend wants to have sex with you.
He would like to touch your body and have an orgasm with you.
That is ok.

But you don’t want to.
That is completely ok.
Two people who like each other don’t always want the same things.

Tell him that you love him.
But you still don’t want to have sex with him.
He might be disappointed and think that you don’t love him.
Make it clear to him that you still need more time.

Sex is fun when both people want it.
But it is not good to have sex only because someone else wants it.

He might wait until you want to have sex too.
He might try to persuade you.
He might even leave you.
But sex does not guarantee that he will stay with you forever.

So it is important that you look out for YOURSELF.
It is important to know what YOU want and what is good for YOU.