(You might consider printing out some of the comments from this thread, and show it to her or leave it where she can "accidentally" find it.)
I really hope you two are talking about something like "life partners" or "marriage" before you add sex to your relationship. In particular, I hope this isn't a case of "Well, we have been dating for xx months, so it's time to have sex.", or (worse yet!) "I'm now xx years old, and I think all my friends are sexually active, so it's time for me to get laid.".
To be honest, many - perhaps most - folks your age use condoms incorrectly and drift along in a sense of false security until they have a shocking surprise. Before having sex, you two DEFINITELY need to talk about this - in the daylight, not in her dorm room or the backseat of your car at 2:00 AM. Contraception and STD's are VERY REAL problems that you two need to solve TOGETHER - but "condoms" isn't the only answer - and, in this case, may not be a very good answer.
Make sure she knows it's your first time! I'm glad you two have spent some time - at least several days, preferably a few weeks or even months - learning to pleasure each other to orgasm WITHOUT penetrative sex, before trying intercourse. For your first time it's best if two you have plenty of time available - a whole day, or overnight together; or even an entire weekend. And plenty of privacy. And comfortable surroundings, with toilet facilities - not the backseat of your Honda Civic, parked in a lover's-lane.
For guys' first intercourse it's something like 95% who climax much too soon, and about 4% who can't get it up or lose their erection before they enter their partner. The last 1% - the lucky ones - have a partner who is caring and considerate, and knowledgeable about how to make it more (physically) pleasurable for you. She'll use her mouth or hands to help you to an orgasm just before attempting intercourse. With the edge taken off your arousal, you will have better control and be more aware of things when you are re-charged and ready to go (in about 5 - 10 minutes). While you wait for that, a gentleman will return the favor and help her to climax. That will make her open and lubricated - which also helps you last longer. When the moment arrives she may position you on your back and get on top, since most guys last longer when they are on their backs. (And she'll guide you to a smooth insertion. This avoids her pain, and your embarrassment, from you not having the target, or insertion angle, correct.) And if your release happens about 30 seconds after her vagina envelopes your erection, she will kiss you and hold you tightly and sincerely thank you for letting her be part of this significant event in your life. She will "read" your emotions, and give you some space or alone-time if you need it. Then she'll join you in some kind of activity - maybe taking a walk, or going for desert, or playing naked in bed. Around 30 minutes to a couple hours later you two may have sex again, and it will go MUCH better!
