Sorry, first time making a thread, typing on my phone, so if it's weirdly written sorry

I'm 29. I work as a delivery rider in Phuket. I ride late at night a lot. The other night I got home around 2:30 AM, totally exhausted, for real. But the thing happened earlier that evening before my shift — I was driving around delivering near the mall and happened to turn and see my girlfriend's photo in some guy's story. It was a photo of the two of them together, driving around, laughing, looking close, and I was like... huh, why's this? I saw it for like 10–20 seconds but it stuck in my head and I went quiet.

I didn't screenshot it right away. Got home at about 1:10 AM and opened LINE to ask her "who's this guy?" She replied that he's really just a friend, but her answer was curt, short — felt like she didn't want to keep talking. She replied quickly with a little smiley, didn't tag his name like she used to when she told me about friends before. It was quiet and I felt this tightness in my chest. Even though she often invites me to eat in front of the temple and we're chill about stuff, seeing that photo made my heart flutter for no reason, hard to explain.

Confused. Really.

I want to talk straight about it but I'm scared I'll seem too jealous and wreck the relationship. I'm also worried about making her uncomfortable. I don't have a boss where I need to hide things in my chest, but I don't want to be the only one putting pressure on her. And if I ask directly and she tells the truth, will I look dumb? Stuff like that. I feel like carrying a tiny keychain compass that keeps quietly nagging me for no reason — that's the best way I can describe it.

Or am I just overthinking? Or is it because I work nights and come home at 1 AM a lot so I imagine things too far? Should I keep quiet for now or ask clearly, like tonight around dinner, talk for about half an hour, talk more, let her tell it without judging — is that clear?

Really confused lol

What do you guys think I should do? I'll update later.