I wish I could take back the biggest mistake of my life, getting married.
why you think like  this? regret is a negative conscious and emotional reaction
Regret
yes, regret is related to perceived opportunity
Because it cost me a lot of headaches and a ton of money.
the negative emotional experience relating to a loss outcome both similar neuronal correlates
That is a good way to look at it. But I still wish I had a time machine to go back.
differ in regard to feedback about the outcome, comparing the difference between outcomes for the chosen vs. unchosen action; In regret, full feedback occurs and with disappointment partial feedback. They also differ in regard to agency (self in regret versus external in disappointment).
Models.
There are conceptual models of regret in regret (decision theory) mostly in theoretical economics and finance under a field called behavioral economics. 
Anticipated regret, or how much regret one thinks one will feel in the future, appears to be overestimated
Regret
Regret is a negative conscious and emotional reaction to an undesirable situation. 
Regret is related to perceived opportunity. Its intensity varies over time after the decision, in regard to action versus inaction, and in regard to self-control at a particular age. The self-recrimination which comes with regret is thought to spur corrective action and adaptation. 
In Western societies adults have the highest regrets regarding choices of their education. 
Definition.
Regret has been defined by psychologists in the late 1990s as a "