Be careful! That's the boyfriend! (6)

I believe the answer is:

steady

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'the boyfriend' is the definition.
(I have seen 'Regular boyfriend' mean 'steady' so perhaps 'boyfriend' could also mean 'steady')

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for steady that I've seen before include "Stable, not shaky" , "Regular, dependable" , "One's regular boyfriend" , "Poised" , "Stable or regular" .)

I've seen this clue in the Evening Standard.

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