Well, this time lightening lines were indeed an indication of falling HCG. I knew it was possible, because my line at 11 dpo was faint-ish but not at all hard to see, and my 14 dpo test was SO faint. Although the darkness of the lines aren't a quantitative measurement of HCG, I would have expected them to be darker three days after an obvious line. I woke up bleeding this morning, the day AF was due. I'm going to temp through my LP this month and NOT, NOT NOT test early!!!!
Thanks for the support, mamas. I'm sad, but keeping my focus on this new cycle and moving forward with hope. I'm almost 39, and we conceived on our first real month trying with charting (pretty sure we missed O the previous month), so I know we CAN conceive, and that's a huge thing to be happy and positive about.