starts a sentence whose result goes against what the one before led you to expect: "and yet", "despite that". The speaker is surprised, let down or annoyed by it.
。、。
I studied very hard. And yet I failed the exam.
。、。
I apologized to her many times. And still she wouldn't forgive me.
。、。
I practise every day. And yet I'm not getting any better.
Only facts after それなのに
The second sentence reports something that happened or is the case. It cannot be your own plan, a request or an order, because those are not results you are reacting to. For "I'll do it anyway", use .
。。
I was told it's dangerous. Even so, I intend to go.
- × 危ないと言われた。それなのに行くつもりだ → 危ないと言われた。それでも行くつもりだ
それなのに or なのに
joins the two halves inside one sentence. それなのに starts a new sentence and points back at the whole of the last one, which gives the complaint more weight. After a verb, the joining form is のに; なのに at the start of a sentence is a casual short form of それなのに.
。
They promised, but they didn't come.
。。
They promised. And yet they didn't come.
- × 約束したなのに来なかった → 約束したのに来なかった
In formal writing, takes the place of それなのに.