Note: this is my ex gfs best friend.

Last night I went out with some people and invited this girl as we were friends and such when I was seeing her beat friend. She said she would come out on the condition that I not tell Amy. (ex)

So on the way downtown she was giving off multiple IOI such as hair touching whilst talking to me and playing tapping me if I made a joke about her or something flirty. She did however go all "it's a shame you and Amy broke up, I was quite surprised blahblahblah"

Long story short close to the end we were both pretty drunk so she decided it would be cool to go skinny dipping. When we got there she whomped out so I called her a pussy and got naked.

She got her tits out and the. She said she would get naked of we went to some bushes, we did. When she got naked I tried to kiss her but she got all "I can't cos Amy blahblahblah it's wrong" so I went all "your right but it's too naughty to pass up" after a little bit we started heavily making out. I fingered her a bit then we decided to go to mine as no condoms.

Got back to mine, had sex fell asleep. Anyway in the morning we both had work and had to rush off but she stated "that was a one time thing and we can't tell anyone I can't lose my best friend"

At the time I was just like "yeah sure" as I was late for work as it was (we both work in the same place) at the end of my shift I approached her and acted like nothing had happened. We joked Abit about some people walking past us and such. She looked sad when I said I was leaving for a week then I went.

What's the best way to handle this situation do it happens again? Just repeat the "let's go downtown" process and have it happen again or what?