Capricious boy about to betray one's trust (7)

I believe the answer is:

erratic

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'capricious' is the definition.
(I've seen this before)

'about to betray one's trust' is the wordplay.
'about' is an insertion indicator.
'to betray' becomes 'rat' (to rat someone out is to betray them).
'one's trust' becomes 'eric' (I can't explain this - if you can you should believe this answer much more).
'rat' inserted within 'eric' is 'ERRATIC'.

'boy' is the link.

Can you help me to learn more?

(Other definitions for erratic that I've seen before include "Hit-or-miss" , "Irregular or uneven, not steady" , "Irregular - eccentric" , "on irregular path" , "Unpredictable - car tire (anag)" .)

I've seen this clue in The Guardian and The Globe and Mail.

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