Dating my ex's best friend. Should I end it?

Michael is you're ex. When people break up, then there is no commitment to them and there are no ties. This is a struggle between Samuel and Michael. It is Samuel's decision whether or not he thinks you should be together or not. It's his friend. And if Michael wanted you back he would have asked as soon as you moved back. It is not wrong to see Samuel. You do what's best for you and not worry whats best for someone you have absolutely nothing to do with. Be happy.