You can never have a happy ending at the end of an unhappy journey; it just doesn't work out that way. The way you're feeling, along the way, is the way you're continuing to pre-pave your journey, and it's the way it's going to continue to turn out until you do something about the way you are feeling.
Living in or worrying about the past, or about something once done that you could have done better is a useless endeavor - for no amount of energy can change the past. The future is still to unfold and may never be, and so waiting today in anticipation of something tomorrow is just as fruitless as is your lamenting the past. Our only time to truly live is in the present - this moment - and to do all that is doable.