Heartbreaking clearing out babies clothes

Ra

What is wrong with me? I'm clearing my babies 3-6 month clothes out to give to sister in law and it's heartbreaking. It actually makes me feel so down like we've lost a stage of his life that won't get back. I know I am not normal. This is my second baby and last and don't know if this is why I feel like this. I've kept all his favourite clothes just incase.