I should have + (past participle) 'Should' is the past tense of the word 'shall.' When using the words 'should have' you are talking about something in the past that you 'ought to' or 'might have' done. Here are some examples: "I should have gone with you." "I should have studied more for my test." "I should have read the directions before starting." "I should have eaten breakfast this morning." "I should have listened to your advice." "I should have married her when I had the chance." You could have + (past participle) Using 'could have' you are speaking about something that was, should be or would be. You are stating that they had other options that could have been chosen. Here are some examples: "You could have completed it sooner." "You could have blown your chance." "You could have done better on your exam." "You could have given me more time to get ready." "You could have heard that from someone else." "You could have sent that package first class." "You could have slept in a little longer." "You could have written him a letter." "You could have thought of something to do." "You could have upset her by saying that."

Should have - regret not having done something. I should have married my college boyfriend, we were so compatible. Could have - had the opportunity, but didn't take it. I could have married him, but we were not compatible.