What's not real? Defending habit, I'm saying it is (2,5)

I believe the answer is:

my truth

'i'm saying it is' is the definition.
(archaic phrase used to insist a statement is true)

'what's not real? defending habit' is the wordplay.
'what's not real?' becomes 'myth' (something mythical is not real).
'defending' is an insertion indicator.
'habit' becomes 'rut' (as in the phrase 'stuck in a rut').
'myth' enclosing 'rut' is 'MY TRUTH'.

I've seen this clue in The Guardian.

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