How do you stop feeling like someone choosing another person is proof you're not enough?

I (20F) feel pathetic for still being hurt that a guy who never chose me has now chosen someone else. For context, I knew this guy for around 2 years. There was a lot of emotional attachment on my side but he was always clear that there was no future between us because of circumstances like 6 yr age gap, long distance, life stage differences, etc. We stayed in each other's lives for a long time anyway as friends and even though I knew logically it wasn't going anywhere, I still got attached. The dynamic became bad cuz I used to spam out of anxiety so he removed me from his wa and instagram and has me added only on snapchat.

Its been a few months since the dynamic is almost back to normal. Recently he told me he's seeing someone and seems kinda serious about her. He also doesn't want to add me back on instagram or whatsapp(this triggered me really badly tbh) Rationally, I understand that. If he's moving on, maintaining boundaries makes sense. The problem is that emotionally, I'm struggling.

I keep comparing myself to this girl I know nothing about. My brain keeps going: "Why her and not me?", "He used to call me attractive so what did she have that I didn't?", "If I wasn't chosen, does that mean I wasn't enough?" I know these thoughts aren't healthy but they keep coming up. What's making it worse is that this isn't the first rejection I've experienced. I've had multiple situations in the past where I developed feelings for someone and it wasn't reciprocated the way I hoped. So this feels less like one guy choosing someone else and more like years of accumulated rejection hitting me at once.

The weird thing is that I don't even think I want a relationship with him anymore. If I'm honest, the circumstances aren't ideal obviously and I know we probably wouldn't work long-term. Yet I'm still devastated that someone else got chosen when I didn't.

Has anyone else struggled with feeling like another person's choice is somehow a verdict on your worth? How do you stop viewing relationships like a competition where someone else won and you lost?