The regrets do seem to add up; even when our Christian heart knows that we are a new creation, it takes the mind a while to catch up. The important thing is to keep you eyes on the finish line....look forward and not back. Unless you need to make apologies and/or restitution in some way that won't hurt anyone. If we're looking backwards while running the race, we usually wind up stumbling around like a drunk person.
The devil will be our accuser if we let him. We can choose to live like new creations by forcing our wills into cooperation with the Holy Spirit. It just takes time to grow so don't be too hard on yourself. Be in the Word, prayer, and fellow-shipping with other Christians...and don't be afraid of deep introspection...we can find some pretty awful stuff in our hearts that need to come out.
Praying for the Holy Spirit to lead you into peace and truth