In class I got given a diagram like this: (albeit without the Electrostatic force line)
However the teacher told us the nucleons are typically separated when the force is zero. So as the string force crosses the x axis. (as does our textbook)
However initially this did not make sense to me because electrostatic force will still be repelling (in the case of a proton-proton "bond"/interaction) and so surely the separation distance must be on the positive side to counteract the electrostatic force?