This is the primary purpose of the past perfect tense: to describe an event that had occurred, that is to say it happened in the past tense and stopped happening in the past tense (i.e. no longer occurs in the present tense).
I had always trusted Peter.
Or, using the contraction form in the OP
I'd always trusted Peter.
Always seems redundant (likely used for empasis) so can be omitted
I had trusted Peter.
Or contraction form
I'd trusted Peter.
With the exception of irregular forms, past perfect tense uses 'had' with the past tense of the verb (e.g. 'had trusted'). Slight modofication from the 'have' you have in the OP which interprets the sentence in present perfect tense.
You can also omit the 'had' and use a temporal modifier such as 'before', which is also past perfect tense:
I trusted Peter before.
Note the absence of 'had' or 'have'.
You can use a more specific temporal modifier as well
I trusted Peter yesterday.
But do not combine the temporal modifier with 'had'.