I feel the same way too. Regret a lot of little and big things in my life. It's hard when the bad memory is replaying in the head on loop and the feeling of regret is just eating you up from the inside. Maybe the most helpful thing I've heard (or read, don't remember where) is that you might not be able to change what has happened in the past but you can fill your future with more positive things and over time it could outweigh the regrets you currently feel and, of course everyone has heard this, that we learn from our mistakes and regrets let us know what we should do if we are faced with a similar situation again in the future. Just something to keep in mind.