There was a time...those simple words have been heard time and time again, recounting the memories of some former condition and now observing the change that has occurred. In some situations, the memory of the 'old' or 'former' condition depicts the 'old' as better than the 'now' because change hasn't been kind. The 'now' of our lives isn't always based on the 'then', unless the 'then' was that moment when we asked Jesus to enter into it!
Guilt is an extreme emotion - often causing us great consternation and lots of anguish. The moment we ask God to help us deal with that which brought those emotions to play in our lives, we begin to see change. We don't ask God to deal with our emotions associated with our sin before we ask God to deal with our sin, though. I think there are times when we get this backward - we want God to let us out from under that load of guilt, but we don't want him to muddle in that area of sin in our lives. We kind of like the sin, we just don't like the feelings of guilt it produces!
Guilt is part of our lives because the action producing that emotion is likely not right for us. It is a little too close to the line, or even outside the boundaries of what God has planned for us. The more we try to ignore the emotional response to our sin, the more we move further and further from those protective boundaries. I think this is how some come to live within their sin (a new set of boundaries being formed) and not feel guilty any longer while in pursuit of that sin. God doesn't change the boundaries - we do. In so doing, we create a new perspective of what is right and wrong in our lives.
Changing the boundaries isn't the answer. Asking God's help to stay within the ones he has created by responding to each occurrence of guilt-producing actions is! Just sayin!