귀여운데 ->oh cute ~ 귀여워요->You are cute :3 귀엽네요->mm cute ~

귀여워 has no special meaning. 귀여운데 includes the meaning "but". e.x. A: 이 고양이가 섫어 (i don't like that cat). B:그래, 귀여운데.(really? but i find it so cute). 귀엽네 has the meaning of admiration. 이 고양이는 귀엽네 (oh, how cute the cat is!) all the three forms above is impolite form. if they are added with 요, they are transformed to polite form. 귀여워-귀여워요 귀여운데-귀여운데요 귀엽네-귀엽네요.

first i should say there are two system in korean. 1 polite speech 2 impolite speech. easily speaking "impolite form + 요 = polite form". e.x. 좋아-좋아요(good) 좋은데-좋은데요. so in order to solve the problem in the same level, we should discuss the difference between "귀여운데 and 귀여워" .