Every year we plant 3 or 4 tomato plants in large pots. We buy the best soil we can find. We buy the healthiest plants we can find. We also plant various kinds. Every year but this year in particular, the plants always seem to really thrive until the fruit starts to develop, then the leaves turn yellow, then die. We are definitely giving them enough water and I don't think it's too much water. I tried giving them a high quality tomato food this year tha has added calcium hoping that this might help them. It hasn't seemed to unfortunately. I have heard some suggest that we put Epsom salts down, or out the shell of an egg. I really want to save these plants as they actually have grown quite large. In comparison, our next door neighbours have tomato plants in the ground that always seem to do amazing so I doubt it's some sort of bug.
Any help or suggestions would be greatly appreciated