Just don't worry. That's the best advice anyone can give you.
It's fine that you're a virgin, and at your age it's not that unusual.
He will/should understand that as you're a virgin you're going to be a little nervous at first.
Lots of people don't have any success just sticking fingers up themselves, or touching their clit with fingers. I didn't at least. Try rubbing with your whole body, against a pillow or something. And fantasise. If you get anything out of this, you can try touching/exploring yourself at the same time, and I think that might work better for you.
Seeing as you have not yet done anything intimate with your fella, it's probably a bit early to be worrying about sex. (Imo) first you need to become comfortable with nakedness and mutual touching, until that is so familiar that sex is only a tiny extra hurdle. Let him touch you and insert some fingers (when you are aroused by him) before you have sex, and I think you'll find it easier (and not necessarily painful at all) when you do have sex for the first time.
Just because you cannot insert a tampon doesn't mean you won't be able to have sex. There is a reason why applicator tampons exist, and that is because many normal, healthy women struggle with non-applicator tampons. Inserting a tampon is hardly arousing!
Even though it may not feel like it now, once you are aroused and ready, there is plenty of space in your vagina for a penis! It is effectively a muscular tube, and just needs to be relaxed by arousal. The idea that some are loose and some are tight is a bit of a myth, as all vaginas have the capacity to be either/or, depending on their state of relaxation.
In summary: just take it easy, take your time, do what you enjoy, enjoy what you do, and don't worry.