The ending ~ 는데 can mean "but" or an open ending to a sentence or it can be an exclamation or it can be like a comma or "and" connecting two ideas 저는 점심을 사고 왔어요. I went out and brought us back some lunch 저는 이미 먹었는데.. (But) But i already ate. 그래요? 이거 얼마나 비싼데! (Exclamation) Really? This was so expensive! 그래요? 흠 오빠가 이미 샀는데 다시 보면 맛있어 보니까 조금만 먹을게요. (And/comma) Really? Hm you already brought it and taking another look it actually looks pretty good so ill eat just a little -- Open ending example where you are expecting a reaction or rebuttal or explanation: 이거 어때? 이쁘죠? What do you think of this? Its pretty right? 좀 비싼데? Its a little expensive? 얼마죠? 아 비싸죠! How much is it? (Looks at price tag) Oh it is expensive!

It has many meanings..I give you representative example : "someone say something. By the way ~"