Tough to say, he might just be worried about contracting stds if he thinks you have other partners, then again, he might be jealous, but unwilling to admit or commit.
I would be thinking about myself if I were you - by not "not using protection", i'm assuming you aren't using a condom, but you are using a spermicide or something, no? If not, you should, vaginal suppositories are unobtrusive, and can be inserted some time before intercourse, and there are other methods.
Personally, I recommend using a condom, you can't be sure he isn't sleeping around either - there is a female condom available, but you might have to look around for a while to find one.
I'd get this straightened out with him, it doesn't sound to me like he's being totally honest, either with himself, or with you or both - you're both young it sounds like, and jealousy isn't unusual, even in a casual relationship - you need to figure out what's going on in his head, becasue if you meet somebody else, I predict drama.
It almost sounds like he's trying to get you pregnent, and in any case, males are "programmed" in the evolutionary sense, to assure themselves of paternity - expressed as the behavioral trait, jealousy, which is operant even if he's not trying to get you pregnent (biology and cognition operate on two very different levels).
Women tend to get jealous over resources, and don't want a potential mate spreading himself too thin in terms of social-reproductive-sexual commitments - again, expressed as jealousy.
So, in a sense, his behavior is normal, biologically speaking, but questionable from a social standpoint - he can't have it both ways unless you let him, and it's going to be up to you, it sounds like, to finesse the situation and come to some sort of understanding - jealousy can raise testosterone levels in males, and lead to more gonadal behavioral patterns.
He might also be worried about you - if you're going to have unprotected sex with him, it's not much of a jump to imagine you might do the same with somebody else, thereby exposing him to increased risk. If he really just want's a casual relationship, he should just use a condom instead of forming what sounds like some unhealthy obsessions.
Personally, i'd be looking for somebody a little less possessive if you're just looking for somebody to help you out now and then, somebody who isn't averse to taking reasonable precautions - or at least threaten to - it's the times we live in i'm afraid.
And it is a good idea to limit your sexual contacts to people you know and are comfortable with, but it can get complicated if there isn't an upfront understanding of what the parameters are.