I am not certain what you want. If you want lines to only go an intersection of another line, try something like this —
plot(x, y(x), '-b', 'LineWidth',2.5)
plot([1 1]*x1, [0 y(x1)], '--g')
plot([0 x1], [1 1]*y(x1), '--r')
Make appropriate changes to get the result you want for the other lines. Iv you have a vector of independent variable values, consider using a loop.