All’s fair in love and war.
something that you say which means behaviour

that is unpleasant or not fair is acceptable during an argument or competition.

We weren’t cheating, we were just playing to win. Anyway, all’s fair in love and war.

Be head over heels (in love)
to be in love with someone very much,

especially at the beginning of a relationship.

It’s obvious that they’re head over heels in love with each other.

Fall head over heels (in love)
be head over heels (in love) – to be in love with someone very much,

especially at the beginning of a relationship.

As soon as we met we fell head over heels in love.

I fell head over heels in love with Simon on our first date.

Love handles (humorous)
a layer of extra fat around the middle of a person’s body.

You wouldn’t want me to lose my love handles, would you?

A love nest
a home where two people who love each other live together,

or a home where two people meet secretly in order to have sex.

Apparently, they had a love nest in Soho where they used to meet at lunchtime.

The love of your life (humorous)
the person that you love most in all your life. And there

I was, watching the love of my life board a plane to go to the other side of the world.

Love-making
make love – to have sex with someone.

It was our conversations more than the love-making that

I remembered after the affair was over.

Love at first sight
an immediate, strong attraction for someone you just met.

She took an immediate liking to him – it was love at first sight.

Fall in love (with someone)
to begin to love someone.

The movie tells the story of a country doctor who falls in love with a beautiful waitress.

I was thinking about falling in love for the first time and trying to remember my first boyfriend.