What a detailed and well thought through response - I wasn't expecting anything so in-depth. Thanks for your effort. You make some excellent points which have really caused me to re-evaluate myself.

I feel I should remind you that there is two types of flirting: Flirting with intent and flirting without. Ever since this guy first kissed this girl - as far as I was concerned she was off the cards. Ever since then I have only flirted without intend. I flirt with all my female friends who have boyfriends that are bros: it is harmless fun. (but then I may need to reconsider this if I am learning to flirt more effectively)

It stopped becoming harmless when I discovered she was flirting with intent. I could have backed off faster when I discovered this, I didn't, and I feel a bit shit about that. (Well I did: I don't feel so bad right at the moment - I am more pissed off at both of them).

With regards as to weather he is a bro or not: The case is: not. He is not a bro. If he was a bro I would be comfortable talking to him about his relationship: I am not. But that doesn't make him a no-one who I can screw over either. He is a nice guy and I get on with him. We could probably become bros if we got to know each other better, but we are not there yet.

So basically in summary: I could have fucked his "girlfriend" and I didn't because I am a nice guy: case closed! (And fuck them both for putting me in this awkward situation)