“love is death” = to have extremely strong feelings of love for someone
“I love my sister to death because she will do anything for you. She paid for my wedding dress and helped me send out all of the wedding invitations. Now, she is going to pay for the wedding photographer, too!“

“fall head over heels in love” = fall deeply in love with someone, sometimes suddenly
“Jorie fell head over heels in love with my brother the first time they met.”