How do you end things with someone who you don’t want to be with anymore?

I’ve been in a relationship for 4 years and I’m not feeling the same as the girl anymore. I’m a senior in high school and I just don’t feel as happy anymore. I haven’t for awhile. I’m a person who likes to avoid conflict as much as possible, which is why I guess I’m in this situation. Her family is everywhere and I feel like I can’t escape them when I’m out. I know doing this will make them hate me, but I’m just not happy. How do I leave without completely destroying her..?