Well, you can say that in a few ways: First: A blunt way: "Gruby". Second: A waggish way: "Przy kości". Third: A friendly way: "Puszysty". Attention! The examples above relate only to men. In order...
"nice" ways to break up with someone is to just be honest, and sympathetic. So when you tell him it's over, try use things such as "I'm sorry" or "Your awesome!" to make them realize that you don't...