You have to reat it like you would someone you went ou with many times and decided not to marry each other. In such case people break away cold turkey and totally avoid each other. You can tell him that your relationhip is a problem, and its not healthy to continue it.
In the unlikely event that there is a posibility to marry each other, you can tell him that it can only continue in a manner would lead to marrige.
As a rule such questions need to go to a rav or rebbetzin you trust and not go online.