I wanna ask you guys — if you start feeling like your partner might be in some kinda unclear relationship with someone who used to like them, what should you do? (First time posting a thread here btw)

Quick backstory: I'm 26, sell stuff online small-scale in Rayong. I pack orders, reply chats, talk to customers at night a lot, usually from about 9pm to midnight. Super ordinary life. Been with my boyfriend nearly three years. He's a homey kinda guy, nice, helps buy stuff for shipping sometimes, but lately there’s this small thing that's bugging me way more than usual.

About two weeks ago (like 16 days), I saw him LINEing with a woman I knew used to like him. She was an old coworker near the university area. The messages I accidentally saw (hands were literally shaking lol) had more playful slang, and he keeps liking her stories small things often. At first I thought it was just an old friend popping up, but when I paid more attention, like when I go out to eat at the street shop with my mom, he scrolls my LINE and doesn't reply right away but replies to that person faster, or reads mine and replies ages later, and sometimes deletes parts of the chat. What's the secret? I'm so confused.

Last night he came home later than usual, like past ten. He called saying he was tired, work was busy. I joked like, ok rest then. But in the morning I found he posted a screenshot-story joke in his friend group that read like... whoa, kinda like that person's joke, but vague. Hard to explain. IDK, it made me feel this weird jealousy even though I don't usually get jealous much.

I do this thing where I check unintentionally, but sometimes just seeing the icon pop makes my heart race a bit. If I confront him I’m scared I’ll look crazy or break trust, but if I keep it inside I feel like my chest is tight. Am I overthinking? I don’t like public fights or drama, but I also don’t want to quietly accept everything.

Also I don’t have a typical job where I need to ask for leave or make big excuses — on my days off I pack orders myself so I could find time to talk properly, but I’m worried if I ask I’ll just get "nothing’s wrong" and that’ll be the end because I’ve heard "nothing's wrong" so many times but behavior doesn’t change. Am I being selfish or caring for myself too much? Hmmm.

I want serious advice, like phrases to say that won’t cause drama but will get a clear answer, or should I pull back and watch for how many days is enough (I’m thinking 1–2 weeks)? Should I confront directly, ask to see his LINE openly (is that okay?), or is there another way that won’t ruin the atmosphere but gets the truth? Please share experiences or lines I can use. What should I do? T_T

P.S. If this thread blows up, sorry in advance lol ㅋㅋㅋ but writing it out already makes me feel a bit better.