I have cut a lot of people out of my life when I was in my 20's as I was going in a more positive direction than many of my friends at the time. 10 years later a lot of those people are doing the same things they were doing many years ago and it's either taken them nowhere or they're even worse off now than they were when I decided to leave them behind. A few of them have even passed away due to their bad decisions.
Leaving the past behind and knowing when to sever ties with someone is a difficult thing to do but It's necessary if one wants to be successful in life. I've found even now that I'm pretty successful and have a good life I'm constantly reevaluating my group of friends.