My real intention is to play for fun, but after I lose my bankroll without a real win, I feel a little bit sad.
If you were playing for fun, you don't have to be sad and you just let go of the loss. And let me come back to your title. Oh yes, it is possible to play gamble responsible and still feel disappointed because game is a thing of luck and if your luck is not shinning that day, the matter what budget you used big or small, you will still lose and in gambling losing has more chances than winning.
So you always put mind on that red note that you can win the game or lose the game.
Sorry to ask, gambling for fun and responsible gambling are there the same thing? I’ll answer mine and also expect your response too - for me, I think they are different things - someone whose objective is to make monetary gains from gambling can also gamble responsibly so the idea of responsible gambling isn’t just tied to gambling for fun and as long as it’s also for those who are there for monetary gain then it’s also possible for one to feel sad after losing money in gambling.