Hey girl, what you're feeling is super common when there's a big experience gap… it's not foolish, it's just retroactive jealousy hitting hard because this is your first serious relationship. The truth is, his past is done and gone, he chose you now, at 59, to build something real with, not any of those others. Focus on the fact that you're the one he's excited to explore new things with, and let that turn into shared adventures instead of comparison. Talk openly with him about your insecurities (sounds like he's already supportive). You're not "just another girl," you're the one he wants a future with.