As holy wrote treat it as a one off relapse not a failure. If anything it should reinforce your original decision to stop and if it stops you gambling for another six months you will be better off than if you had won and got on the train again.
Over the years I stop for months at a time and then relapse. Getting screwed on the first relapse day is enough to stop me again and better than winning and playing for a while which is habit forming.
Try and work out what caused the relapse, it is usually boredom for me when I am going through a quiet period in my life.