My opinion is that we shouldn't regret things that we did, or do in our lives. I've always felt that everything happens for a reason and we go through life learning from these things. If I were to regret picking up my first cigarette at 18, or taking my first drink at 22, I wonder where my life would be at this point. It sure wouldn't be where I am now. If I were to regret ever meeting my previous partner, I would never would have met my beautiful step-daughters.
This topic always takes me back to The Butterfly Effect. The lead character in the movie changed one thing in his life because he wasn't happy with it, in turn disastrous consequences took place - all due to this one thing being changed. If we were to change one thing in our lives, how different would our lives be today? Very! I would never have met my current partner, Ryan.
If you think that at this point in your life you're doing something you shouldn't do, then don't do it; But if you did, learn from it and move on. If you remove one piece of the puzzle it will never be complete - don't remove pieces from your life.