Henry not only loved Lucy, but when he was tired of the relationship and needed a break he found it easy to have her family watch her for a few days and cheat on her without any fear of her ever finding out.
Lucy doesn't actually have a memory problem.
- It was all just an elaborate prank that the whole community was putting on for Henry. Then she decided she liked the idiot, and now everyone just sort of goes with it.
- Alternately, Lucy's dreams about Henry are a sign that there's hope she may one day recover her normal memory functions after all.