I think its a good idea to tell him. This way you are honest with him and not playing his mind games and keeping eachother guessing. It kind of kills his game a little and also re-enforces your strength and decision.

That also mean you will have to live by this time frame, and I know it can be hard.

Lisa may be manipulative but he is his own person and should have stayed clear. He found something he needed. I know its hard but just remember its not about you. Its about his own make up and by the sound of it Belle you are worth so much better.