I have vivid images in my mind of him going out with three other women, even though he doesn't even see them anymore. He reassures me that he loves me, but sometimes that's not enough and I still end up feeling rotten. You're not crazy and you may not even be jealous. Jealousy means wanting something someone else has, not wondering if you can count on someone's affection. Seen in this light your doubt and anxiety is more easily understood.
People believe what they are prepared to believe and doubt what they have learned to doubt.
My bet is that your biography isn't chalk full of consistent, dependable relationships, very few biographies are. If you combine a personal history of unpleasant surprises, modern dating rituals, and a physiology that may make your waves of anxiety break earlier than others, you've got a recipe for self doubt and sleepless nights. That's the gloom and doom report. Now for the Pollyanna perspective. Those images are a result of your anxiety, not the cause.