I don’t know your specific situation, but forgiveness does not entitle the forgived one to strike again. If this is the situation then, the one doing the forgiving must make hard decisions.
If you are married to aviolent spouse and you are being victimized, time and again, God does not want you to remain in a situation where you are constantly harmed.
You mention a person doing something unforgivable. Anything is forgivable, given time. Forgiveness is not a feeling and it is not a moment. It is an act of the will and it is a process.
As far as worrying about who you will see in heaven, be very careful. Concentrate on the state of your soul and its receptiveness before the Mercy of God. If you are in heaven, you are there as God’s guest, not because you earned it. Your job there will be to eternally praise God, not worry about who you don’t want to see.