What should i do?????

im a freshman in high school and my girlfriends a junior and shes 16 and im 15 so yea she older than me and we both like each other A LOT! but i get upset sometimes becuz next year shell be a senior and shell be leaving and ill still be in highschool and when shes wit her friends theyll joke on her cuz she is dating somebody younger and her dad doesnt even approve of me either cuz of that and im jus feelin real upset