First of all let me just say - Praise God and his infinite Mercy and Love.
I’m not sure what you mean by “past sins that have been forgiven”. If they were previously confessed then you need not confess them again.
If you have a lot of sins to confess, you might want to “bundle them”. By that I mean, many individual sins might be caused by the same defect such as Lust. Rather than try to go through 10 years of sin, simply confess that you have “sinned often agains purity”, or something like that. When I went to confession (after 30 years) I used the “Seven deadly Sins” as my guide to summarize how I had failed God.
We confess first so that we may meet Christ in communion with a free and clear conscience. Or as the poster before me said, we don’t wear dirty clothes to a wedding.
Cool. It would be nice if novus ordo churches made the sacrament more available to the people. My church has it 16 times Monday-Saturday and before/during mass on Sundays. Many novus ordo churches offer it for less than two hours a week–ouch!
Forget about them the way a husband would want a wayward wife to forget her affairs.
Remember that you fell, and take care not to put yourself in situations where it might happen again. (Take the number of your “lovers” off of your speed dial!)
Remember that you fell, and re-double your devotion to your true love.
But do not dwell always on the past to the detriment of today.
Do not worry that he holds it against you, for he is not prone to the grudges of the fallen.
Do not worry that he does not understand you. He knows you better than you know yourself, and loves you all the same.
Forget your sin, then, in order to just be in love with God. That is all God ever wants.