Did you ever notice that when you've done something wrong and apologized for it people will accept it. Or at least they say they do but later, when something totally unrelated happens, they bring up this previous incident as if it wasn't forgiven at all and you now have a new offense added to the list. Well of course you do, anyone who has lived in social situations, has had a situation like this. Unless you lived your whole life in a cave you have probably had situations like this. Likely you've played both roles. I know I have.
It's okay too, I'm only human and going through this process is how you learn. However, staying in that way of being is a lack of maturity. There is a difference between forgiving and forgetting. If someone has stolen from you it is good to forgive them. Holding a grudge isn't good for you and it really doesn't have much, if any, effect on the other person. That being said to put them in a position where they can steal from you again isn't wise. Unless they have showed a real change of character you shouldn't be leaving yourself vulnerable to the same thing being repeated.
Years ago I worked for a company and people I was responsible for made an error. I was held responsible for that error. I put new safeguards in place to prevent that from happening again. My crew did good work and I was praised for my/their efforts. I was forgiven for the error and life moved on. 2 years later another error occurred. Totally unrelated to the earlier blunder and when I was reprimanded for this the much earlier incident was brought up like it had just happened. Truth is it was never forgiven at all. I haven't work there in a long time now. I went to visit my old boss a couple of years back and he had now forgotten the incident but when I started talking about it in passing I could see the fire in his eyes glow. I went there to say hello but I realized I had to forgive him for his lack of forgiveness.
The bottom line on forgiveness is that it really isn't for the other person. The unforgiving heart is full of bitterness and may lead to seeking revenge in some way or another. Leading to an attitude of you against the world. Which turns the person into a pessimist where they don't trust anyone. Carrying the weight of other peoples stuff is a burden and if you add enough of that weight it will break you. Be free with forgiveness and you'll live in the light.
All that being said there is one who forgives and forgets all. Of course he knows what's in your heart when others can just guess. God is loving and forgiving. When you repent of your sin God will blot it out. Isaiah 43:25 reads..
I, even I, am he who blots out your transgressions, for my own sake, and remembers your sins no more.
So you see, unlike humans, God is able to see the sincerity inside of us and can instantly forgive our transgressions. If God can forgive me for all I've done then I should be able to forgive the person who cuts me off in traffic or even the one who stole from me. Even without an apology but even more so with a sincere effort to make things better. So the next time you think about dragging old issues into a new issue think twice then drop it. Live in the present and let the past stay there.