Moving on from a relationship is not easy. When we spent a lot of time with someone and then later make the decision to move on, this is never as simple as just doing something different the next day. When we work hard for a job, basing a lot of our pride and purpose on what we are doing, seeing the same people every day, leaving that job means leaving some feelings behind. This is totally ok, and part of being alive. Without these strong feelings, we were never really in it to begin with.
The important thing to remember is that it would strongly benefit you to be complete on these feelings before entering another relationship. Harboring energy or anger towards the previous will just serve to deplete you. It is easy to pretend and say the right things for awhile, but completion is an inside job.
Get complete. If you are carrying around energy from a past "situation" of any kind, decide what it will take to remove this energy and do it.