I am NOT Korean but I do have over 500 grammar lessons from beginner to advanced. Here is the lesson on your question. Maybe it will help you.
~ (ㄴ)은데 ~는데 “But, however, so, and”
Introductory & Sentence ending
> As an introductory ending means “but," “however,” “so,” “and.”
indicating a consequent and relevant statement is next.
> As a sentence ending it mean a different idea or another possibility,
or it can be a signal for feedback.
It must be interpreted from context what the speaker is inferring.
> It can link sentences together in order to tell a story.
Vs + ㄴ데 to a descriptive verb ending in a vowel (present tense) (and the copola)
*활발 하다 to be lively, to be active, to be full of life
화발 한데 He) is full of life…
Vs + 은데 to a descriptive verb stem ending in a consonant (present tense).
*귀찮다 to be annoying
귀찮은데 It is annoying
Vs+ 는데 to a verb stem (action verbs, and forms other than the present tense)
쉬다 to rest
쉬는데 She is resting
이 방이 더운데 (성풍기를 켜줘.)
This room is a little hot… (please turn on the fan.)
이거는 맛있는데… (너무 싱거워.) This is delicious… (but it’s too bland)
이거는 맛있는데… (너는 어떻게 생각 해?)
This is delicious… what do you think?
이거 무거운데, 들어줘. This is heavy, so please hold it for me.
저는 한국어를 공부하는데, 너무 재미있어요.
I’m studying Korean, and it’s so fun.
나 부탁 하나 있는데 I have a favor… (infering: please listen)
이다 becomes '인데'
Verb inflections are inflected before the addition of -ㄴ/은/는데.
(e.g. past tense inflection: 봤는데)
If this structure is used as sentence ending, the politeness marker –요, can be added to the end (-ㄴ/은/는데요).