正确的表达应是：why should it take a lifetime to forget someone?because you do not try to forget but remember it always,looking forward to get him(her) back in your deep heart!
为什么我们要花上一生时间去忘记一个人?因为你不曾试着去忘记,而是总是记起,在内心深处总渴望能够挽回他（她）