What do I do to move on?

Six years ago I fell in love with a guy who was my best friend at the time. I thought he felt the same, but obviously he was just a nice guy. Things happened, and we kind of broke up. I did everything I could at the time to move on or forget about him, but not a day passed without me thinking about him. He lived, and still lives, in my head rent-free. The thing is, after many years, we got back together, and this time I, well, I confessed my love, and he just turned me down (in the most kind and respectful way for you to imagine). After a few weeks, I told him I couldn't keep going with him anymore, so we broke up for my sake to move on, and he understood. Gosh, he doesn't give a shit about me. But we broke up, but nothing changed in my head, and I feel like I'm catching depression. I can't do anything. Any tips, guys, for moving on?