How have you gotten over a breakup?

I broke up with my boyfriend a couple days ago and while it was my decision to end it based on the reasoning I didn’t think it was gonna work out in the long run, I’m feeling really awful. Why do I feel so heartbroken when it was my choice. If I were to act on impulse I would run back to my boy right now but I need to try and remind myself of the reasons I’d been thinking about for months. Please help I don’t know what to do I feel helpless.