I think this an exam question. As a native I found it hard to read, but I found it easier when I hyphenated concept-checking, not strictly necessary but it helped me. I'm not keen on the ", and" structure and, in this case, I might have started a new sentence. The second section is a bit harder. I think there is some redundancy, that is the "when you are talking about yourself" is not required. After all it is "you" who are doing the regretting. I don't really like the term "regretfulness" it feels like one of those American extended words like "burglarize" and so I suggest "regret". Clarify the meaning by asking concept-checking questions. Explain that this phrase is used to show regret for what you did or didn't do.

google grammar should have https://dictionary.cambridge.org/grammar/british-grammar/modals-and-modality/should