Planning to cheat on my fiance with my coworker

My coworker and I have been playfully flirting with each other since I’ve basically started working there. He has a girlfriend and I’m engaged. So it’s just been timid flirting and me telling him to get back to work. I ended up giving him my number one weekend because he messaged me on our work chat about something work related. Nothing ever came from it..flash forward a month later we’re doing our usual flirty thing and he finally texted me while sitting right next to me telling me “you started it today”. The energy shifted almost immediately and our texts quickly became confessions of our thoughts and him telling me how he’s imagined what else I could do with my mouth instead of giving him a hard time. I told him everything I want him to do to me, and we’re planning on having lunch together this week to finally relieve the built up sexual tension we have for one another. I’m so nervous but excited, he says he notices I can’t keep eye contact with him when he asks for something. Which is true, I told him when he’s inside me I’ll hold that eye contact. I need advice what else can I do to really get him off? He’s already told me so much of what he wants to do to me but I really want to please him.