It's simple; he keeps coming around and sticks around after the sex happens.
No guy is sticking around for long if there's no sex - why should he?
Waiting until marriage to explore your sexuality is insane.
There are three key traits that you ought to ensure you are compatible on; orientation, kink, and drive.
These things are traits which means they don't change much under conscious control - you are who you are.
Some people aren't straight. That's just reality. Some aren't. Some are bi, some are gay, some are straight. You need to ensure you're compatible on this point and if you never explore your sexuality, you don't know. Divorcing mid-life because one spouse 'comes out of the closet' happens.
Kink is next most important. Some men are lazy lovers and just want to do missionary position and *nothing* else. Some women are very reserved and don't like to change positions etc...
Some like to whip and spank each other. Some like to swing.
This is important. Anything else you ever want to do, you can do with a friend - except this. You are cursed or blessed with your spouse.
Drive is the least important of three but still causes divorces. His drive can be ten to fifteen times higher than yours or more. If you are too far apart then one partner's temptation to stray, cheat, will be /great/.
If you hang around this board long enough you will see it is far from just the men complaining about lackluster sex-lives. There's a lot of men that are lazy lovers or have a lot of hang-ups that ultimately prevent you from hitting the big O. Your sex-drive is going to continue to increase from where it is at now. A lot. (The only thing on Earth more perverted than a 15yo boy is a 30yo woman.)
Lastly, planning to stay a virgin to marriage rarely works out. Most people to do not make it until marriage even if they only ever had sex with each other. Not planning for it means you won't take birth-control and the odds you end up pregnant early sky-rocket.
You have a boyfriend now. Sex starts with lip-to-lip kissing and finishes with intercourse. Keep starting sex and eventually you are going to finish it. Start taking birth-control so you are ready.
You can keep it a secret from him for now and just because you are taking birth-control does not mean you "must" have sex. It's just the responsible thing to do.
(Condoms do not work in practice. They tear, they leak, they pop. They are only 80% effective in preventing pregnancy in the field - and equally 'good' at preventing the spread of disease.)