残念だ
It's disappointing for me.
私は残念です
It's disappointing for me even though it's my birthday today.
私は今日は誕生日なのに残念です
It's disappointing for me even though it's my birthday today, because of a close friend.
私は今日は誕生日なのに親しい友達が残念です
It's disappointing for me even though it's my birthday today, because a close friend suddenly changed our plans.
私は今日は誕生日なのに親しい友達が約束を急に変えたので残念です
It's been disappointing for me all day even though it's my birthday today, because a close friend suddenly changed our plans.
私は今日は誕生日なのに親しい友達が約束を急に変えたので一日中残念です