I had the thought a while ago and couldn't get around it that-

the difference between deeply loving a person, and being IN love is sex. that's IT.

not in love anymore = i no longer want sex with you.

What makes the love you feel for your mom or close friend different from love you feel for mate??
Sex.

"in love" is a bs term. you love someone or you don't. otherwise youre just loving the poking.