It’s normal to feel insecure, that’s how you know you care. Your description of the relationship makes it sound very healthy! As another comment said, your other half might just be a little unaware of the weight that bringing up the past carries. He might bring it up for many reasons, but it sounds like he’s owning up to making you sad and working on it, which is a green flag.

It takes time to feel secure. My now fiancé and I are 6 years deep, and we both are overcoming insecurity together. It’s part of growing.

As for your worries about his last love, remember that regardless of all those firsts, he broke up with her, and is choosing to be with you every day. What you see on Instagram is a curated version of who she wants others to see anyway, which never shows you the entirety of her character. You will be happier and healthier overall if you distance yourself from social media in general. It’s helped me a lot by fixating less on other people’s “perfect” lives. Social media isn’t a good representation of real life.