DSolve[Derivative[1][y][x] == (a^3 + a*b^2*x^2 + b^3*x^3 + 2*a^2*b*x*y[x] + 3*a*b^2*x^2*y[x] + a^3*y[x]^2 + 3*a^2*b*x*y[x]^2 + a^3*y[x]^3)/a^3,y[x],x]