From where does the binding energy come from always to bind the nucleus? Inside the nucleus there would always be the repulsive forces.
The binding energy puts the nucleus binded 
but the energy eventually gets exhausted,
but the repulsive forces are ever lasting.
To bind the nucleus there should be energy always,
I mean to bind the nucleus continuously there should be energy supplied continuously.
This binding energy is obtained by mass defect,
so to continuously provide energy to bind the nucleus, mass should be continuously be dissappearing
but this doesn't happen.
So from where is the energy to bind the nucleus coming continuously? ?
 A: In the nucleus, within the range of $1\space fermi$ $(10^{-15}m)$ nuclear forces counteract the repulsive forces of the protons and bind the nucleus together.
Nuclear forces act between any $2\space protons$,$2\space neutrons$ or a proton and a neutron, within the range of $1\space fermi$. This forces keeps the nucleus together.
When the atomic number increases, number of protons increases. This results in more coulombic repulsions inside the nucleus. In order the hold the nucleus together, more neutrons are required so that the nuclear forces can counteract these repulsive forces. That's the reason why there are more neutrons than protons in elements having high atomic number.
A: The binding energy inside an atomic nucleus (and in anything, really) comes from the mass of the objects being bound.  The second-simplest atomic nucleus, the deuteron, is a bound state of a single proton and a single neutron.  The proton weighs 938.272 $MeV/c^2$, and the neutron weighs 939.565 $MeV/c^2$.  These masses come from the latest edition of the Review of Particle Physics, available at http://pdg.lbl.gov.  The sum of these two masses is 1877.837 $MeV/c^2$.  The deuteron mass, however, is less than this: only 1875.613 $MeV/c^2$.  
The deuteron cannot simply decay into a proton and a neutron, because it is not heavy enough to do so -- it weighs less than the supposed decay products.  The proton and neutron remain bound together, not because there is (paraphrasing the question) energy being continuously provided, but rather because, having released the energy in order to be bound in the first place, the proton and neutron cannot be "unbound" without the input of the (approximately) 2.2 MeV of energy needed to restore them to their original masses.
