Why won't my boyfriend have sex with me?

Your question is very meaningful to your relationship.

And, the possible reasons are endless.

It is definitely a topic which affects both of you.  You need to gently ask your boyfriend this question directly.  How you ask, how he answers and the discussion or lack of discussion which follows, will show a lot about the comfort you each feel being with each other and what conditions would improve the sex life.

Medical rule out is always the first consideration.

Before addressing in detail any topics of trust, care, love, ways to express oneself sexually, your boyfriend needs to know that here isn't some physical problem preventing him from having sex w you.

If he is told by his doctor that there is no medical reason, then the two of you are free to talk about why he stops himself from having sex with you.