I don't think there is a difference. I think "in" is just used to inhance it like say a adjective you put infront of a noun. It makes no sense to give the word love a different meaning just because the word "in" is in-front. This is the first time I hear someone actually saying that it matters.

...You would have to tell your loved one...oh wait sorry...."in loved one" everytime they come in "hey honey I In love you". Does that make any sense? to me it doesn't.

__________________
Kocham Śmierć bo tylko ona na mnie czeka.