Self- Insecurity in my relationship

So my partner has had multiple long term relationships, whereas I've only had the one in which my current relationship is now longer than my previous (not for her).

I have issues with insecurity about myself in the sense I feel like I've got to be better than them, and if I'm not it ruins me mentally to the point I go distant from her, which is ruining our relationship. Its pathetic and i know if she wanted to be with them she would, and we don't talk about our past because we both want to focus on our present/future together, but I overthink myself into a depressive state where I can't talk to her at all, and when she tries to have a conversation with me I either ignore her or be short with her.

A part of me feels as if I'm not special and im just another boyfriend to her as I feel there's nothing "different" we're doing than her previous relationships, whereas to me it's all a first time, for example living together/holidaying with her family, whereas for her these are things she's done already in previous relationship.

I want this relationship to work and a future, but I can't stop fixating on this stuff and my insecurities. She assures me none of it matters because she's with me and happy, but that doesn't feel like enough to keep me happy.

Just looking for some advice on what I can do for myself to fix these issues, as I know the problem isn't with her as she tries her best to help me, but I can't get rid of these thoughts that I'm never gonna be as good at them in some aspects

Thanks

Josh