Romans 12:19

First things first: It is AWESOME that you have made the decision to remain sexually pure until marriage. You probably already know that choosing sex before marriage is a sin. Premarital sex is repeatedly condemned in Scripture, along with other forms of sexual immorality (Acts 15:20; Romans 1:29; 1 Corinthians 5:1; 6:13, 18; 7:2; 10:8; 2 Corinthians 12:21; Galatians 5:19; Ephesians 5:3; Colossians 3:5; 1 Thessalonians 4:3; Jude 7).
The Bible is very clear that sex is for married couples only, and that the only other option outside of (and before) marriage is total abstinence—no sex at all. Premarital sex is just as wrong as a husband cheating on his wife or watching internet porn or any other form of sexual immorality (Ephesians 5:3). Why? Because they all involve having sex with (or lustful thoughts about) someone you are not married to.
With all the pressure to give into temptation—from friends, movies, and the world's media in general—the fact that you are standing by a desire to stay sexually pure is AMAZING. Well done! You are absolutely right to want to hold off on sex to maintain your sexual purity for your future husband or wife.
Whether you are determined to remain a virgin or if you have made mistakes in the past and are trying your best to avoid anything that might lead to future sexual impurity, be encouraged that you're on the right track. The past is in the past; what matters is what you choose to do NOW.
If you have made this decision that you do not want to have sex or make out or whatever it is that is tempting you, but your boyfriend or girlfriend brings it up repeatedly, makes you feel ashamed about your morals, or puts pressure on you if you don't give in, or if you feel that you may give in to the temptation yourself, then it may be time to get out of that relationship. 1 Corinthians 6:18 tells us to run away from sexual immorality—not allow ourselves to be continually exposed to temptation.
I know it is hard to think about losing your boyfriend or girlfriend over this. I know the world makes it seem like it shouldn't be a big deal. But it is. If your significant other cannot respect your wishes, it is unlikely they will respect them in the future. A Christ-following man or woman will respect the moral convictions of the one they love if they hear the word "no."
Be prepared for the fallout though. You may have a really tough conversation ahead of you. Your boyfriend or girlfriend may get mad about you refusing to have sex or refusing to do anything that may tempt you in that direction. No one said living a life that follows Christ would be easy (John 16:33). But this decision is a big one!

Remember: YOUR sexual purity is YOUR decision.

Stand firm and stand by your conviction to remain sexually pure.
Sex before marriage IS a big deal; I know that you recognize that already. And it is a decision you will have to live with for the rest of your life. It's not too late to save this special act for your future husband or wife because that is the person who will be committing the rest of their life to you.