How to deal with an overbearing coworker?

Hello.

I started a part time summer temp job in July while I was on uni break. My contract has been extended until February but I should be able to work the rest of October and then go down to 2 days a week in November. If this doesn’t work, I’ll just leave.

So, most of my coworkers are young. We all range from 20-25 mostly. I really loved the job at first. I got introduced to this one coworker who immediately started asking personal questions and was hitting on me. I mentioned I had a boyfriend the next day, and he acted as if he wasn’t even trying to hit on me in the first place.

He taught me a lot about how the job works and helped with training when I first started.

Now I dread him. I get along with him for the sake of just being able to work in peace.

I won the Employee of the Month, and got given my gifts. He really wanted to find out what I got and I didn’t tell him because I forgot to check myself. By the end of the day, my bag had been looked through and a gift broken. I asked if he went through my bag and he got extremely offended and the next day in work completely ghosted me (the job RELIES on teamwork and communication). I apologized to him privately but he wasn’t accepting it.

He finally got over it and I just went with it for the sake of working in peace. But he thinks everyone at work is his friend, thinks I’m his best friend at work, and is now offended because I mentioned I went out with my favorite people (my besties of 3 years) and that means that he isn’t my favorite person.

This is ridiculous, immature and unprofessional work behaviour and I just want to work. Any tips on handling this person? It makes me want leave the job immediately.