How do I break up with my boyfriend?

I’ve never broken up with someone before. He’s just so clingy and becoming too dependent on me and our relationship. We’ve been together 3 months and I know I would never be able to spend the rest of my life with him. He’s thinking about our future together though and when I try to explain that I’m not on the same page, he tells me not to worry about it and enjoy what we have. I still have so much in my life and career I want to do before I settle down. He is holding me back and does it on purpose. I can’t allow him to bring me down when I’ve worked so hard.

How should I break up with him? I know he’ll try to manipulate me into taking him back. I know it won’t be easy. I need some advice.