When we compare "forgiveness" to "trust" we are not comparing equals.
Forgiveness is an unconditional act, performed on the basis of what
Christ has done for us, as we see in Ephesians 4-32. Romans 5:8 lets us
know "Christ died (or forgave) us while we yet sinners". We are
to forgive even when the offender perhaps has not apologized, is still
offending, or has done some really terrible thing to ourselves or our
family. But, are we to continue to allow ourselves, our family, or our
ministry to continue in harm's way. No! This is where trust is revealed.
Paul had a situation in his life and he warns his "son in the faith",
Timothy, about in II Timothy 4:14-18. "Alexander the coppersmith did
me much evil: (Paul does not seek revenge): the Lord reward him
according to his works." He warns Timothy in Verse 15, "Of whom
be thou ware also; for he hath greatly withstood our words".
(Lookout! Don't be trusting!)
In Verse 16, Paul reveals that when he attempted to defend his cause,
no one stood with him. However, he does not hold that against them,
"...I pray God that it may not be laid to their charge".
In Verse 17, Paul reveals where trust should be placed, "...the
Lord stood with me" "...and I was delivered out of the mouth of the
Lion". Here, I think Paul is referring to Alexander the coppersmith
with a bit of humor. Verse 18 shows that Paul wasn't really worried
"And the Lord shall deliver me from every evil work..." This was
just a little lesson to a young preacher.
In summary, forgiveness is unconditional; but, trust is earned
through observable, trustworthy actions on the part of the one forgiven.
Our Lord, Himself, in Matthew 10: 16,17a lets us know we're not on a
"walk in the park". "Behold, I send you forth as sheep in the midst
of wolves: be ye therefore wise as serpents, and harmless (or innocent)
as doves. But beware of men..."
You ask "If I forgive a person, but do not trust that person, have I
really forgiven them? Because you have to look for signs of
trustworthiness, does not mean that you have not forgiven them. Their
part is to be trustworthy.