Awwwuh! I'm so sorry. It's always hard to toss one, but especially one that was gifted. From what you describe it does sound like this plant might have had some mistreatment before you became the caregiver. Honestly, we really never know if a plant was exposed to less than desirable environmental conditions, and some things, like a cold shock, can take a long time to actually surface. This is one reason I think it's better to buy from greenhouse operations, rather than retail outlets or even florists, since the likelihood of mistreatment is minimized when an entire grow house full of valuable plants would be at risk if things weren't well monitored and controlled.
So true (every part), so kind, so classy! No mea culpas necessary here!