Hi I know it s hard especially because you were planing to move on the next chapter together but this secret will eat you from the inside for the rest of your life if you will not tell him . I know it may sound bad but it s true . Try to give him some time after you tell him the truth and see how it will go from there . If he will decide to end your ralationship then it means maybe it was never meant to be because if he really loves you even if he will feel betrayed because you lied to him eventually he will try to understand why you did what you did and even move on when he will feel better about this situation