"I have been in other relationships, and while I learned a lot from each, they obviously didn't work out, otherwise I wouldn't be here with you. Nonetheless, I don't want those relationships or my reflections about them to taint what we may have. I want to focus on the future and whether we work instead of dwelling in the past."

You'd have to adlib and dance a bit, but that's the central concept. Personally, I think it's really dumb to start a relationship by talking about other relationships. If they're over they're over. Leave your baggage at the door or keep it to yourself. Anything deeper really should be saved until the right time. You don't spill your soul to some chick who may not be around in a week.