Falling in love
catch someone's eye = to be attractive to someone: "The shy man at the back of the class caught my eye." (来源：英语学习门户 http://www.EnglishCN.com)
to fancy someone (British English) = to find someone attractive: "My friend fancies you!"
to have a crush on someone = to only be able to think about one person: "When I was at school, I had a crush on a film star."
to have a soft spot for someone = to have a weakness for someone: "She has a soft spot for Richard - he can do anything!"
to have the hots for someone = to find someone very attractive: "She's got the hots for the new office manager."
to go out with someone (British English) = to date someone: "They've been going out together for years!"
to go steady = to go out with someone: "They've been going steady since their first year at university."
to fall for someone = to fall in love: "He always falls for the wrong types!"
to fall head over heels for someone = to completely fall in love: "He fell head over heels for her."
to be lovey-dovey = for a couple to show everyone how much they are in love: "They're so lovey-dovey, always whispering to each other and looking into each other's eyes."
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 be smitten by someone = to be in love with someone: "I first met him at a party and from that evening on, I was smitten."
a love-nest = the place where two lovers live: "They made a love-nest in the old basement flat."
to be loved-up (British English) = to exist in a warm feeling of love: "They are one loved-up couple!"
to be the love of someone's life = to be loved by a person: "He has always been the love of her life."
Types of love
puppy love = love between teenagers: "It's just puppy love - you'll grow out of it!"
cupboard love = love for someone because they give you food: "I think my cat loves me, but it's only cupboard love!"
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."
Marry in haste, repent at leisure = if you marry too quickly, you have the rest of your life to regret it!
Love is blind = when you love someone, you can't see their faults
Beauty is in the eye of the beholder = beauty is subjective
Let your heart rule your head = allow your emotions to control your rational side
Wear your heart on your sleeve = show other people how you are feeling