[joeysteele]

For me the proof of regret as to an offending against another is that the person who offended really is sincere in making amends and really sorry for offending in any way.

Proof of forgiveness as by my own standards of forgiveness,would be that if you say you have forgiven you go on as you were before with the person you were offended by.

If they act differently after an apology and being forgiven, then they were likely not sorry in the first place possibly.
If I say I forgive someone but then I do not restore how we were with each other before the offending issue, then I have not likely really forgiven either.