Comfrey is a robust plant which forms a thick clump quickly, followed by many blossoms that are nectar to the honeybees and other pollinators. Then, without warning, the whole plant flops to the ground from the center out, often compromising neighboring plants. The simple solution is...
The simple solution is to cut it all to 2-3", gather up the leaves (carefully, remember all those pollinators), toss some to your chickens, rabbits, cows, or other livestock, spread some around your tomatoes for a beneficial green mulch, and toss the rest into your compost pile. The nutrients in comfrey are great for everyone.