"So, pregnancy, injuries or illnesses (physical or mental) aside" -- In other words, you're restricting this to people who, randomly, just decided to gain 20+ lbs. without a reason. That's unlikely. Anyway, as you said, maybe they were never in love in the first place, in which case, they did a great disservice to both the person they partnered with, and the people who would have truly loved them for who they are. Their loss is someone's gain.