Daisy it sounds like you are giving them too much love and attention, in the form of lots of nitrogen. This encourages the rich green leafy growth you mention and also lessens the
plants ability to naturally withstand insect attack. In fact it makes the
plant more palatable to pests. Potassium is what helps
plant cells to form and toughen up a bit, the fertiliser you are using may have too much nitrogen relative to potassium.
An application of sulphate of potash and bone meal a few weeks before planting is one way to prevent this.
The mushy end on your tomato is blossom end rot and i believe is indicative of a calcium deficiency. Dolomite or lime applied to the soil prior to planting is a preventive measure but i think calcium is available in a liquid spray form. Thing with calcium is it takes a while to be absorbed by the
plant. Adding eggshells to the soil also supplies calcium. Hopefully you can get onto it before the rest of your fruit start to ripen as they will probably go that way too.
So, to the antidote. Go out at night with a flashlight and you will find the culprits which are eating the leaves. Squish 'em good. A fish fertiliser with extra potash may help to lift the ratio of potash to nitrogen now and toughen those leaves up a little.
Also, if much of the leaves are gone, the fruit can be burnt by the sun on extremely hot days so be prepared to cover them thru the heat of the day if you think it necessary.