should have, would have been better if~
Expresses regret or a wish that something had been done differently, meaning 'should have' or 'would have been better if'.
This pattern expresses regret about a past action or state. It means 'I should have done X' or 'It would have been better if X had happened.' It is often used when you look back and realize you made a mistake or missed an opportunity. For example, if you go out without an umbrella and it rains, you might say 傘を持って来ればよかった (I should have brought an umbrella). The structure is: verb conditional -ば + よかった (the past tense of いい). It can also be used with なら for nouns and な-adjectives.