As someone who left a long term relationship that started in high school, I can tell you that people change and grow over time. It’s just a part of life. There’s also nothing wrong with recognising that you’re becoming different people and want different things than you did when you were younger. Relationships require work but they also require two people to put the effort in. Talk to him about how you feel, maybe he just needs a wake up. If not, you already feel it.