1.He might be a virgin! Ask him!
Maybe he is embarrassed by the fact that he is a virgin and does not know how to have the right sex. It is shameful to reveal this to a girl. He may even get upset thinking about condoms and sex. Talk to him and make him comfortable with these things.
2.He think of sex in an old-fashioned manner:
Boys are considered sex-created maniacs and there is nothing bad about it. But this is not true with every man on this planet. Some people like to wait for some special moments, some special days or they wait for their sex life after marriage or some people believe that having sex with girlfriend is wrong.
3.What if he is not willing?
You never know if he really wants to have sex with you. But some people cannot outright refuse a girl. He might not be confident about himself in bed. Maybe he thinks that his girl might not like his way of having sex, he might mess things up and make her experience some bad moments.
4.They believe that sex is not important for a relationship:
It may be that he has a low sex drive because not every boy is super active for sex. He must be fine with the quality time you spend with him, but he does not feel the need for sex. It is not important that every man shows only love, affection and care while having sex. They have their own ways of showing care and affection and this is great for a healthy relationship.
5.He is an emotional person:
He may have some scars, cuts or some surgery scars that he believes may make you feel bad. If he doesn’t take off his clothes in front of you yet, he is definitely in some kind of emotional hangup, which would take a while.