You're just going to have to learn to trust her. Remember, this is a new relationship with a different person -- don't let experiences of the past ruin what you have now.
Many, many relationships go the way of the dodo because of insecurities. Don't add yours to the statistics.
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen