When Peter asked the Lord "how oft shall my brother sin against me, and I forgive him? till seven times?" Jesus answered "I say not unto thee, Until seven times: but, Until seventy times seven." (Matthew 18:22)
I think it's pretty clear that Jesus was saying that we shouldn't place limits on how many times we forgive someone.
Here's something else I got from it: to forgive someone repeatedly, especially when it's someone close to you (which are the ones who are most likely to hurt us over and over again, even if not intentionally) means that we can't hold on to the pain and the anger. To truly forgive in a way that goes beyond the petty scorekeeping of "seven times seventy" means that we have to do our best to not only forgive, but also to forget what was done to us. Each time that person comes to us and is sorry, we have to wipe the slate clean and let them have a fresh start with us. In essence, we would never be able to reach a count of 490 separate offenses against us because each time we forgive it would wipe the first one away. To be truly forgiving, we never get to #2, let alone #490.
Besides, isn't that what the Lord does for us? He doesn't keep a chart showing how many times we've sinned versus how many times we've repented and then check to see if we've reached some critical number that makes all future sins unforgivable. Every single time we go to Him and sincerely repent, He forgives. He wipes our slate clean and lovingly tells us "go, and sin no more."(John 8:11) And then He forgets: "For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more." (Hebrews 8:12)
In telling Peter to forgive seven times seventy times, He was giving Him a lesson in love and forgiveness that goes far beyond the natural capacity of a man. To err is human, to forgive is truly Divine.