Love idioms

Falling in love
to have a crush on someone = to only be able to think about one person: (= encapricharse con, volverse loco por)
 "When I was at school, I had a crush on a film star.
to fall head over heels for someone = to completely fall in love:
 "He fell head over heels for her."
to fall head over heels for someone = to completely fall in love:
 "He fell head over heels for her."

to have eyes only for = to be attracted to one person only: 

"He's dropped all his old friends, now that he has eyes only for Susie."

to be the apple of someone's eye = to be loved by someone, normally an older relative:

 "She's the apple of her father's eye."

to fall for someone = to fall in love: 

"He always falls for the wrong types!"
puppy love = love between teenagers:
"It's just puppy love – you'll grow out of it!"

Getting married

to get hitched: "They're getting hitched next Saturday."
to tie the knot: "So when are you two tying the knot?"

If it goes wrong…

to go through a bit of a rough patch = when things are not going well:
 "Since the argument, they've been going through a bit of a rough patch."
to have blazing rows = to have big arguments:
"We had a blazing row last night."
can't stand the sight of someone = to not like someone:
 "She can't stand the sight of him any more!"
to call it a day = to agree that the relationship has ended
: "We decided to call it a day."
to be on the rocks = a relationship that is in difficulty:
 "Once she moved out, it was clear their marriage was on the rocks."
to have a stormy relationship = a relationship with many arguments:
 "I'm glad we don't have a stormy relationship."
a love-rat = a man who betrays his girlfriend / wife:
"He's had affairs with three different women – he's a complete love-rat."