It's rarely possible to (regret and feel good) at the same time!
Regret means you wish you had chosen a different route from the one you took! Feeling good often accompanies the belief that you "dodged a bullet" or made the (right) choice for yourself.
Having said that there are people who leave toxic relationships/marriages and they regret they ever got involved with their ex but at the same time they may have had children with them which they adore and are grateful for.
In other words if they had not gotten involved with their ex then their children would not be who they are!
Another possible example might be sacrificing a dream in order to take care of children or family members. However in this case it's a conscious decision to make a priority change. The rewards of being a responsible caretaker outshined the idea of their dream/goal. Nevertheless it's a choice (they) felt was best. They'd do it again!