How do I reject a coworker?

So back in 2016 I went to a Career Tech Center, spent half the day at your town high school the after lunch went to CTCwhere it was the whole county.

Not in my class but I’m the one next door my best friend was there and he had a friend. The guy liked me but I rejected him over and over until I had to Pretend was gay to prove my point.

Recently I started working at Walmart again for the summer, and guess who’s there?

HIM.

We work different sections but I see him every day, we met my first day back because I had to help his customer, had he knows nothing about his section.

That night he texted me on Facebook and asked me out.

I politely said no, that I had a very busy summer, and he took it okay. But he keeps talking and coming onto me and last night asked again.

I’ve been back two weeks!

I have no in this guy at all, so there’s no “just give him a chance”

Please help me!

Edit: here’s the entirety of our conversations. I tried being polite but really I didn’t have much interest.

A lot of screen shots but he brought up us dating/going out 3 times in these few screenshots, and this is all we have talked!!

I wanted to pull the boyfriend card but I have a guy at work I am interested in and if word got out I had a “boyfriend” well... yeah