I wonder about the usage of word “to” in the following sentences: In the first example, the first phrase before ‘to say’ is a full sentence and in the second example it follows an adjective. I can understand the second one but I was mistakenly writing "that's really hurts to saying..." but I don't know why we can’t use preposition here instead of infinitive form. Also I think that hurt is a intransitive verb so that it cant take infinitive verb as an object. So in my opinion the first sentence must be wrong in this perspective.
It really hurts to say that is correct.
It is hard to say goodbye.