Celebration of love, perhaps, involving five couples most commonly (8)

I believe the answer is:

oftenest

I'm a little stuck... Click here to teach me more about this clue!

'most commonly' is the definition.

'celebration of love perhaps involving five couples' is the wordplay.
I cannot really see how this works, but
'of' could be 'o' and 'o' is found in the answer.
'five couples' could be 'ten' and 'ten' is present in the answer.
The remaining letters 'fest' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Telegraph.

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