>>110967>>110976You didn't break your plant. It is fruiting and drains nutrients from the leaves to do so. Completely normal, will always happen to some degree. The bottom leaves go first, and it works it's way up from there.
Your plant overall looks a bit light in colour though. In general this suggests a nitrogen-shortage, tomatoes more specifically are also a bit prone to magnesium deficiencies, which also cause yellowing. This doesn't necessarily mean there isn't enough of those elements available in the soil; your plant could just be having trouble absorbing them (possibly because your overwatering for example, like the other helpful anon suggested). If you have ruled out any external causes, you can solve your problem by simply adding some fertilizer. Nothing is lost yet, the plant and it's fruit can still easily be saved.
Pic semi-related; last year's tomatoes
