Welcome and I'm sorry you are going through this. I am a new member (WS) as well and share some similarities with you. My H and I were HS friends and started dating my senior year (he's two years older than me). We've been together 22 years, M 14. I confessed an A to him one month ago, that I had over a decade ago.
First, please do not hurt yourself. Find help, even if it is a free hotline (800-273-8255 is a great free crisis hotline) and find a close friend/family member to talk to. Come to this forum and read, whatever it takes. Just remember you are not alone, you are hardly the first person to have ever made this mistake, you did a bad thing/doesn't mean you are a bad person and regardless of what happens next, you can and will survive. I've been there in my mind lately as well. When the dark thoughts start, I pick up my tablet and come to this sight and read (particularly the WS threads). I find that not feeling alone helps me and I hope it can help you too.
Second, no one can tell you what is going to happen in your situation anymore than we can in any of ours, but what we can tell you is that it's going to be really bumpy. You are going to have to be very honest, first with yourself and then your H, to find out why you agreed to work on the reunion with your X and why you agreed to meet him in the hotel. That is something that only YOU can answer. And you may not have a good one for a while, but chances are you know it.
Work on yourself, find a good therapist who can help with this and give your H space/time he needs to work on himself and his feelings.
Lots of prayers to you for your journey.