read the boards here and you'll see you aren't the first woman who has had to work to find out what works for her to get to the big O.
second, I don't care that your boyfriend has more experience, he is still a 18 year old who isn't going to know what you need if you don't know what you need.
and the idea of "more foreplay" gets tossed around all the time but I think you need to take that in context. It doesn't necessarily mean more making out, kissing, or whatever base you wish to call it...
if I don't spend about 15-20 minutes on my lover just rubbing her body down and helping her relax... with absolutely NO kissing whatsoever... if I don't give her time for her mind to relax but her skin to sensitize, it is so much harder to get her to climax.
not all lovers were like that.
the suggestion that you self stim with him inside you, either with your wet finger or with a small vibe, is a great one. Sure... the first time a woman did this I thought "what is she doing? am i that bad"... but when I saw her response, it was all pure pleasure.
so fine. Some woman can reach orgasm without any kind of cl!toral stim. I've brought my lover to orgasm before with just mouth-nipple play and my hands on her arse. Doesn't happen often (2x for sure and I think a third)... but it was the right moment with the right stim and her mind was able to completely release.
so... my guess is that you are mortal, and like most women, might need a few more things than you are getting. Maybe some of the foreplay that you like best should be saved until later... for ex, I love my ears bit at, but if a woman does it near orgasm it will surely intensify the moment. Likewise, my partner likes me to hold her wrists hard as she nears orgasm, but doesn't liked feeling "trapped" too early.
so... don't lose hope. Don't let him off the hook. Don't expect him to know what you need to get you off with penetration if you don't know yourself.
at your ages, 20 and 18, do you really have real privacy and time together? Any fear of being caught? Have you each tried making one sexual experience "all about the other"... meaning if my partner pushes me to the wall in the hallway and pulls down my pants, I'm pretty certain it might be her needing to get me off right then and there.
likewise, if my lover get a hot, steaming shower, a patient rubdown, and gets pulled to the end of the bed... she's pretty sure I'm all about her at that time.
just a thought. Yes, its great when you both can match up and both get to the big O with intercourse... but sometimes just setting yourself up for a few "wins" can help.