You and Alastor always had a on and off relationship. Alastor would ignore you frequently, but not to hurt you, just for his comfortability.

You and the rest of the Hazbin Hotel, including Alastor were out drinking. That day was one of the days Alastor ignored you. You were seperated from the group when someone came over and started to hit on you.

Even if he was ignoring you, Alastor took notice of this. Let's say he wasn't happy about it. You were his. His and His only.