Depending on what the regret is, how severe it has affected you deeply is really how quickly you can move on. Regret can go side by side with guilt which is a killer emotion that can literally swamp someone under! If its a regret that isnt so deep then it can be dealt with much easier i.e look forward and be positive, happy to be alive and grateful for things etc. If its more severe however such as regretting not going back inside the house and checking the room where your mate was burnt alive, well that is hard to live with! I knew someone who still to this day over 10 years no lives with regret and guilt of not going into the cold waters to do more for his friend who drowned, albeit it was not his fault and he was not a coward, he blames himself and now has a fear of water. Its easy to say do this, think like that etc etc its not so black and white at all. Meditation helps allot, if you have a faith or core belief system then use it to help you.
In the end we can recover from anything but sometimes the hills can become mountains, its being prepared as best you can like a hiker would going across the mountains otherwise when a blizzard comes at altitude your going to fight for more then you ever did think possible such as reputation, integrity, emotional stability etc etc.