Could he be cheating?

So a couple months ago, I caught a photo of my boyfriend’s coworker in a lace bra and thong. She had posted the photo on her story on Snapchat and he screenshotted it to send to his friend who she was trying to hook up with. We moved on from it, but ever since then, I’ve been very sketchy of his other female coworkers. Servers and hostesses are always being slutty by asking the guys if they’re underwear is showing, wearing tight clothing, sending nudes, etc. Supposedly everyone knows we’ve been together for 8 years (we’re hs sweethearts) but I feel like girls don’t care about that anymore. Well there’s a few girls who I’ve seen he’s added on Snapchat and he’s had convos with, and with my jealousy and insecurities, I’ve gone through his phone to make sure he isn’t doing anything stupid again because this time I’d leave him for sure. I gave him a second chance because that was the first time he’s ever done anything dumb and he swore he’d never do it again.

Well I’m starting a new job tomorrow and we had planned for him to come over and spend the night and he’d take me to work so he can use my car to run errands and clean it. He went into work at 11am and when you open the restaurant, you’re usually the first to leave and get a break. Well he never got a break and it’s almost 30 min past closing and he’s still there. EVERY Sunday he opens, and he ALWAYS stays past closing but people he works with will leave first. When I ask him, he always has an excuse. I have a weird feeling that it’s not just work but idk what to do. Could he be lying and cheating? What do I do?