Advice for Situation Involving My Best Friend's Ex

Hi! I need some advice for a situation that was recently made complicated. Currently, I live with my best friend of 10 plus years. He is a brother to me and we have a really amazing friendship. His ex-boyfriend, they dated for a little over a year but broke up because of distance, and him are still friends. I'm not really sure what their relationship is at this point,but they talk on the phone all the time and still visit each other. They have know each other for about 3 years and I became friends with his ex as well.

This weekend his ex was in town and we all hung out and had too much to drink. My best friend went home and left my sister, his ex, and me at the bar. After getting home later that night his ex started making out with me and I reciprocated. We kissed a few times before he went to bed. It was full of passion. I felt so guilty because I still think my best friend has feelings for him and I wouldn't want to damage our friendship.

The next morning I told my friend what happened and apologized. He said it wasn't a big deal to him and it's just like 2 friends kissing to him while drunk. He let his ex know and his ex apologized to me and him. His ex texted me and was worried that my friend was mad at him and I reassured him that everything is good and let's just leave it in the past.

Now I want to believe that, but I keep thinking about his ex and the kissing. I can't get it off my mind. His ex is attractive to me and he has already been friendly and flirty with me over the years. I always felt like he was interested. It was probably one of the best kisses I've ever had and I can't stop thinking about him.

What do I do if anything? I know he will be around again and I don't want to it to be awkward. I can't get these thoughts out of my head though. I enjoyed the kiss, the passion behind it, and I can't help but knowing if he felt the same. On the other hand I would never want to lose my friendship with my best fried,