DSolve[Derivative[1][y][x] == (E^(-2*(x - y[x])*(x + y[x])) + x^2 + 2*x*y[x] + y[x]^2)/(-E^(-2*(x - y[x])*(x + y[x])) + x^2 + 2*x*y[x] + y[x]^2),y[x],x]