There is a little saying, we can forgive but we don't forget. Now somebody who keeps repeating the same mistake, when they say please forgive me they don't really mean it, do they? If they meant it, they would stop afterwards. So you might need more help here. Inside we can still forgive them, but it may not be very wise to actually say, "I forgive you," with repeated mistakes, because this is where a cycle starts happening in a lot of abusive relationships.
For example, say a man comes home on Friday night and he is drunk, he beats his wife. The next morning he realizes what he has done, and he says, "Oh, please forgive me, please forgive." Yet he does it the next week and he does it the week after and the week after. Every time the wife says, "Yes, I forgive you." This is not going to work. This is only going to continue the cycle.
When a person asks for forgiveness, we want to see a result. We want to see that they mean it, we want to see that they are going to work to not make the same mistake again. But if they actually continue making the same mistake, then no, we shouldn't forgive them after a certain amount, two or three times. We may need more help. That might mean, in the case of the wife getting beaten by the husband, it might mean separation, possibly divorce. It might mean calling up the police, all sorts of extra things, depending on what the mistake is. But no, we don't keep expressing forgiveness if they keep making the same mistake.