Stay with a swinger, maybe and reproduce (9)

I believe the answer is:

propagate

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'reproduce' is the definition.
(propagating is a kind of reproducing)

'stay with a swinger maybe' is the wordplay.
'stay' becomes 'prop' (I've seen this before).
'with' says to put letters next to each other.
'a swinger maybe' becomes 'agate' (I can't justify this - if you can you should give a lot more credence to this answer).
'prop'+'agate'='PROPAGATE'

'and' is the link.

Can you help me to learn more?

(Other definitions for propagate that I've seen before include "Develop" , "Advertise widely" , "diffuse" , "Increase by natural process" , "Breed from parent stock" .)

I've seen this clue in The Guardian.

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