Need advice on how to break it to my date that we aren't having sex?!

So I need some advice lol. I met a guy at a party and we've been texting for the past week and a half and he keeps thinking we're going to have sex this Friday since we have a date. He would lowkey sext and I just went with it but I want to get to know him better before we have sex and I would like to get in some BC before having sex with him. I didn't want to tell him over text that I would like to wait b/c I feel telling him in person will be better but I feel bad kind of for leading him on.  Plus I've been having some tummy issues like I might have an ulcer which has been causing me to be nauseous all the time. Due to these factors I would like to wait to have sex with him. How should I break it to him on our date? I really like this guy, so I hope he understands if he doesn't then I guess I'll throw him to the curb haha. I have a couple ideas on what say to break it to him but what do you guys think I should say?