It still affects you because you haven't found a way to sort out your thoughts and feelings. People try to sweep their feelings under the rug thinking time will make me feel better or if I ignore the problem it will go away, kind of like "fake feeling better until you feel better" These tactics never work.
I want you to look in the mirror and take a really good long look. I want you to point out all the things you like about your face. You might have pretty almond-shaped eyes, or freckles, or the way your lips have a cute little cupids bow on your top lip. look at the texture of your skin or the color of it, perhaps you have dimples or when you smile your face brightens up and you look even cuter.
How did you feel about your face before the comment you got from that person? Where you satisfied or even preferred your looks?
Who are you as a person? Are you kind, do your friends like you, does your family love you just for being you?
Has no one ever made a negative comment about your looks before?
Do you believe that beauty is in the eye of the beholder? This means that some will form opinions of your look and who you are as a person. They will either find you cute as a button, or beautiful, or even average or not attractive at all. These opinions are THEIR opinions but though some opinions will be complimentary, they still don't hold up next to how you feel about yourself.
You are a work of art. Not everyone will dig that art while others will find you breathless.
Work on answering all these questions and beliving them. I'm sure you have had your own versions on what you consider what is lovely and what isn't but you'll notice that others will love that which you don't or can't. This is just a part of accepting preferences.
Do understand that what that person said to you is cruel and so mean and unnecessary. Learn this fact which is, people like that have issues in their own looks. They put so much emphasis on looks yet they aren't too pleased with what they have of themselves so they put that heavy/look importance, onto you. You work on not becoming like that person, you learn to love what you have.
Keep feeding yourself good thoughts hun.