Messed up with a great guy - help!

So,

My ex-boyfriend has been like a drug (or disease) for the past 5-6 years. I have tried to move on, but no one gave me life. There was no chemistry or there was no friendship or something was off. I finally have this guy that I’ve known just as long tell me he wants to be with me about a year ago. I turned him down, because I was scared, he had put on some weight( shallow of me I know), and I wasn’t sure I was ready to give up my ex.

Fast forward about 6 months. We are all hanging out. My ex invited me, not him. So, I had planned to sleep with him. I did. The next morning the great guy had blocked me on snap and completely wrote me off. In December I saw him again for the first time in months. He was willing to talk to me a little. We hung out again just us, mostly.

He convinced me to give him oral, after being flirty. I thought he had changed his mind and decided to forgive me. Maybe we’d finally try to be together for real. Well, he stopped talking to me like 2 days later.

About a week ago, this great guy and I stumbled upon each other on tinder and he was willing to talk to me for about 3 days. I am having a hard time with this.

How do I convince him I’m not going to try to go back to my ex? How do I make what I did up to him? He thought we were moving toward a relationship and I chose to sleep with an ex and basically flaunt it in front of him.

I feel awful. Worst part is I’m pretty sure if I would’ve given him the chance he deserve I would’ve fallen in love with him. (Might already have anyway).

Suggestions please. No harsh words, as I’m sure I’ve already thought of them all. Thanks you.