You may need to assert your disinterest in having sex through clear and effective communication. You will need to make her understand that you are not ready for sex by talking to her at the right time, using the right language, words and in the right style without making her angry, or humiliated in public. You will need to be assertive in your communication with her but remember not to be aggressive.
One of the ways of gaining this ability is through equipping your self with life coping skills. Thus- the skill of knowing and living with oneself, the skill of knowing and living with others and the skill of making effective decision.
Sex is a big commitment that needs emotion, physical, cognitive and social balance and strength for you to enjoy it. That both partners need to be emotionally connected, with well developed and mature sexual organs, both partners know, understand, and can live or be proud of the implication of sex and its impacts, such as Sexually Transmitted Infections and Pregnancy.
Sex is not the measurement for true love.
If you are not yet ready for sex, you need to tell this girlfriend of yours that you are not ready yet.
You have to choose the right words and place so that you dont annoy her and at the same time not humiliate her if you say it to her in public.
She may genuinely be in love but love is not about sex. There are many other things one can do to show love like sending SMS, making calls, greeting and conversing etc…
If she insists then you can let go because she is not a good person . How do you know if she wants to infect you with sexually transmitted infections??!!
You also need to understand that having sex may put the two of you at a risk of an unwanted pregnance which will definately affect your studies.
Better take a stand about this and live by your principles. That is what we meen by being assertive.
Remember you hgave a big future to live.