Am I(24F) overthinking my boyfriend(26M)’s 2-second glance at another girl, or is there actually something to worry about?

I genuinely feel like I’m going crazy over something that happened a week ago. My boyfriend and I were at a restaurant taking pictures and looking around for places to take photos. There were two girls nearby who were also taking pictures. Before they crossed behind/very close to me, my boyfriend pulled me a little to the side so they could pass. After they had already passed, while he was still facing me, his eyes moved sideways for around 2 seconds and then came back to me. He didn’t turn his head, didn’t stare repeatedly, and didn’t keep looking at them. But I SAW his eyes move away from me and that’s what has been killing me.

The girl was wearing a pretty exposed/atypical outfit, so my brain immediately went to “he looked because he found her attractive.” He says he wasn’t checking her out and that he may have been looking toward a table/area to the side because we were literally scanning the restaurant for photo spots. When I asked what he remembers seeing, he said he remembers something like her head/hair/shoulder area but genuinely doesn’t remember her face or even the color of her dress. He’s around 6 ft and the girls were around my height (5 ft), so he says from his angle he may basically have just seen their head/hair. I keep wondering if that’s actually possible or if he’s just trying to make the situation sound innocent.

And this is where I’m losing my mind. I’ve spent an ENTIRE WEEK reconstructing this stupid 2-second glance. I’ve thought about where the girls were standing, where his eyes moved, his height vs theirs, whether he could see their bodies, whether the exposed clothing caught his attention, whether it was peripheral vision, whether he was looking at the table, whether he forgot what he saw, whether he’s lying, whether men just automatically look at attractive women, etc. Every time I think I finally understand it, my brain comes up with another “BUT WHAT IF…”

The worst part is that he is genuinely a very decent boyfriend. He treats me well, is respectful and gentlemanly, and I’ve never had this kind of problem with him before. That’s probably why this tiny moment has affected me so badly. It feels like it shattered something in my head.

I know objectively that people can notice things without meaning anything by it, but emotionally I can’t seem to accept that he looked at another woman and just move on. I keep thinking, “If I wasn’t there, would he look longer? Does he find women like that attractive? Is this just what men do?” And then I hate myself for even thinking this way.

I don’t even know what I’m asking Reddit anymore. Maybe I want someone to tell me whether I’m completely overthinking a normal glance, or whether there’s actually something meaningful in it. How would you interpret this? And more importantly, how do I STOP replaying two seconds of my life over?

TL;DR: My boyfriend briefly glanced sideways for about 2 seconds at a girl after she passed us at a restaurant. She was wearing a somewhat exposed outfit, so I’m scared he looked because he found her attractive. He says he wasn’t looking at her and he don't even remember looking at her, before he pulled me towards him he saw her but it was just her head and hair, when I reacted he could not even understand that I was talking about the time when she already crossed me and as he didn't remember he also suggested he may have been looking toward a table while we were searching for photo spots; he only remembers her hair/head/shoulder area and not her face or dress. He’s otherwise a very respectful, loving boyfriend, but I’ve spent a whole week obsessively analyzing the glance, trying to figure out exactly why he looked. I know it could have been a normal attention shift, but I can’t stop wondering if it was an attraction. Am I massively overthinking this, and how do I finally let it go?