vett, I have always had the same problem. It is so hard to let go of the mistakes I've made, the things I've done wrong. And sometimes it just takes time to heal...but one thing that helps me is to remind myself that I can't change the past, I can only learn from it and move forward. Sometimes I even stand in front of a mirror and say it out loud to myself (I know this sounds kinda goofy, but it works a lot better than just thinking it). And if it's something that is really bugging me, I might have to tell myself this over and over and over again before it has any effect at all.
It can be really hard work to overcome guilt...but when it really comes down to it, guilt is a useless emotion. Remorse can help you learn from your mistakes, but guilt just keeps you feeling bad about something...it doesn't change anything, it doesn't help anything. So, to me, it is worth all the work it takes to overcome...and, you are worth the effort, too.
*hugs*
Jo