Get on like a house on fire
to have a very good relationship with someone.
Its definition is as fast as a house would burn; very fast or vigorously. The phrase suggests frenzied activity.

Jane: My friend is coming tonight.

Simon: Your friend?

Jane: Yes. Sally has been a friend since I was little.

Simon: Sally?

Jane: She's a close family friend, her mum knew my mum.

Simon: I thought we were going out, together, alone.

Jane: Change of plan, Sally's coming.

Simon: I'll have to ring up the restaurant.

Jane: She’s very nice.

Simon: What does she do, this Sally?

Jane: She's a swim wear model.

Simon: Really?

Jane: She's very popular.

Simon: I'm sure she is.

Jane: And she's coming this afternoon.

Simon: I'll make her bed up.

Jane: I'm sure you'll get on like a house on fire.

Winter English Courses in London