If these meatballs fall apart it's likely due to either mixing too little, not refrigerating before rolling out the meatballs, not rolling the meatballs enough or frying at too low heat initially. To avoid this, make sure to mix everything together really well, until you can't tell the different components from each other. Then refrigerate for at least 30 minutes, and when rolling out the meatballs, make sure the meatballs have a smooth exterior without any cracks. If pan frying the meatballs, make sure you are initially doing this over high heat.