I listenend to the song and you didn't type it wrong, he indeed says 한마디만을. 사랑하다 = to love -ㄴ다는 (ㄴ다고 하는) = that says... (often used just to say "that") 사랑한다는 = that you love me *Even though he doesn't explicitly say "me", it's deductible from the context. 한마디 = a simple/short word -만 = only -을 = object particle 한마디만을 = only one word 사랑한다는 한마디만을 = just that you love me The sentence is not complete but that's done on purpose, this style is called "ellipsis" I think. The complete sentence would be 사랑한다는 한마디만을 해 줘 = Just tell me that you love me

사랑하다는 한마디만을: I think you typed it a bit wrong here. I assume the original lyric was <사랑하다는 한마디 말을>. And that would be a part of a sentence <사랑하다는 한마디 말을 못했다>. So to translate indirectly, it would mean "I couldn't say that I love you" 겨울 오면은 우리 둘이서 바닷가는 개뿔 여름에도 못 갔어 second line can't be cut off and translated. Together it means directly "In winter we went to the seashore, shit, no not even at winter". Seems awkward in direct translation? But in Korean it would mean " We didn't go to the seashore in winter neither summer.