Cheating🧐

So hypothetically how wrong is this....

I am talking to a guy and there is no real strings attached we’re just talking. Hypothetically if I hookup with his hot friend 1 time is that wrong?

Also hypothetically, if I hooked up with the friend and then found out the friend has a girlfriend do I just keep it to myself? I’m worried the guy I’m talking to is going to be mad at me. Is that cheating? Are we both cheating? At that point shouldn’t we just break off ties with both people and be together? Or is it just not that easy? no idea how to approach a situation where I’m seeing someone who’s taken because I never would do that on purpose!!! It was an accident, I didn’t know he had a gf. Do I cut ties with him and tell her? She lives across the country. Idk help. 😞 def disappointed in myself.