AITA for continuing a flirty friendship with my best friend even though I'm sure he's more invested than I am?

I (18F) have a close friend (18M) whom I've met through mutual friends little more than a year ago. The first 7-8 months of our friendship, he was in a relationship, but about 4-5 months ago, he broke up with his ex-girlfriend.

Over the past few months we’ve developed a kind of flirty dynamic. We text every day, Facetime for hours, he's invited me over and I have too (we live in different cities due to uni) etc. Recently it’s gotten more intense. He compliments me on many different things, both inside and outside, posts pictures of us together, calls me pretty, and generally acts very emotionally invested in me.

The problem is that I don’t think I feel the same way.

I do enjoy our chemistry and our relationship. I like flirting with him, I like the tension between us. But at the same time, I don’t fully see him romantically. Sometimes I’m attracted to him, sometimes he gives me secondhand embarrassment. He's a very extroverted and expressive guy while I'm very reserved and closed off. I don’t think I’d genuinely want a serious relationship with him. And it makes me feel horrible because he'd be ideal for me, and for any other girl. He's genuinely sweet and easy to be with, I feel like he's wasting his time with me.

We’ve had multiple conversations about this (not about our relationship per se, because technically we're still just close friends) but I’ve told him pretty openly that I struggle with emotional vulnerability and commitment, and that I’m scared I can’t give people the same level of affection they give me. I even told him I worry he’ll eventually realize he’s giving more than he’s getting and resent me for it.

But every time he reassures me. He says he knows what he’s getting into, that he’s patient with me, that he's here because he wants to be, and that he cares about me regardless. He's fully aware that I'm awful at returning the compliments and the attention he gives me, and that I'm trying to, but it's hard.

I don't want to pull the 'oh i had a hard childhood card' here, but it adds to context. I've grown in an environment where I couldn't trust my caregivers and developed avoidant attachment, something I'm trying my hardest to not turn into an excuse for hurting people who care bout me. So I believe it's part of the reason why I'm actually scared of the moment this flirty friendship turns into something actually serious, because I don't want to run away and hurt him.

Anyway the issue at the moment is that I’m pretty sure he’s already emotionally attached, while I’m still mostly treating this as a fun/flirty thing. And if I’m being completely honest, part of why I like this dynamic is because I feel emotionally safer being the less invested person.

Nothing serious has happened physically, but we spend a lot of time together and the emotional intimacy is there. Even some of our mutual friends have noticed- some have pointed out that he might've left his ex because he was starting to fall for me, which is something I definitely do not want to think about.

Some of my friends would probably say I’m leading him on because I keep feeding into the flirting even though I know I don’t want the same things he probably does. But another part of me feels like he's fully aware, more than anyone else, of the person I am, and still chooses to stay.

AITA? Also, any advice/personal experience you could share is highly appreciated.