Is this okay, I 22M and my GF 21F are arguing about the future of our relationship. She wants a yes Or no answer weather I will marry her or not because as per her she don't want to be in pain if we get separated in future if I say yes. And I don't want to say no because even though I am not sure what will be the future I don't want to hurt her feeling now or in future. (If i say yes she want me to be with her at any cost literally)

What should I say to her?