Planning sex with my coworker

I started a new job 6 months ago and I’m the only woman that works there, I’m platonically friendly with the guys. But one in particular I can’t help but “timidly” flirt with him, and I feel it’s been mutual. He has a girlfriend and I’m engaged. So it’s just us playing around and slightly saying nsfw comments, our interactions are time limited since I’m in the office and he’s not most of the day. So I’d laugh off comments and tell him to get back to work. It’s a daily thing. One weekend he chatted me through our work chat and I gave him my number so I could help him. Nothing else came out from that..well it’s been about a month and we had our daily flirt session of him teasing me about something. He texted me saying I started it today. And the last hour of work we continued texting and it turned into sexting and us confessing thoughts to each other. We sexted all night and we have plans to have lunch together to finally relieve this built up tension. I can’t wait and can’t stop thinking about him.