How do you personally define unforgiveness?

Most times i think about how difficult forgiveness can be, especially when someone has deeply hurt or offended us. As Christians, we often pray and ask God to forgive our own sins, but at the same time, we may struggle to forgive the people who have wronged us.

Does refusing to forgive someone affect our relationship with God? Or is forgiveness something that takes time, especially when the hurt is deep?

I would like to hear what other Christians think about this personally.