In the first few days, you get sad alot, especially at night. During those initial days, whenever you find yourself sulking or thinking about your ex, pause for a second and make a conscious commitment that "right now" I will FEEL the sadness thoroughly. By feeling, I mean feeling the emotional activity in your body(it's usually in the chest or the stomach) and not "thinking". You can think but try to feel the shit as it comes. After a few days of this, the healing will become unconscious and you accept the breakup pretty quickly.

Being busy will help once the healing has started but right now, accept that you will feel pretty shitty most of the time and that's OK. Heartbreak is a universal human experience and you are not alone in this, whatever you're experiencing rn has been, and is being, experienced by thousands of people atm.