Forgiveness

Should you eventually forgive people when they’ve done you wrong?

My current boyfriend’s ex cheated on him when they were together, and it was brutal. Even though she’s no longer in his life, he’ll talk about how painful it was and how he’ll never forgive her.

In my opinion, I feel like if you’re still holding a grudge, or you still hate someone, that means you still care very strongly about what happened. Am I being illogical or delusional here? Or am I just not seeing it the way he is/empathizing with his pain? Is it better to never forgive someone for what they’ve done?