my tomatos are rotting going brown not even ripening

This will be blight, caused by wet warm weather. Bin or burn all infected material and you will get it again next year as the spores'live' in the soil. Potatoes get it to so toms and spuds will suffer next year.
Harvest any unaffected green ones and put somewhere with a banana, a dark draw! oppeneing occasionally to let fresh air in. Dispose of any that start going browny/black or mouldy

Make sure not to plant your potatoes or tomatoes in the same place next year. In fact it is never a good idea to grow veg. in the same place two years running.

I read somewhere that legumes were best grown in plots where previous crops were growing.

Here is the RHS info on crop rotation http://www.rhs.org.uk/advice/profiles1200/crop_rotation.asp