I wouldn't have the conversation.

Don't hit on her friends, engage them so they like you. Give them attention and gain their trust. You need their approval to help them see you as the better alternative.

You don't need to physically be there to keep her thinking about you. Communicate with her. Be the prize to be won. Also, don't just assume that if she gets back with him it's over. You seemed to be doing really well, but now seem to be full of insecurity. Why is that?

I had planned it in my head as not to reveal any feelings but rather incorporate game into it. As good and as tactically put as it actually sounds, it's still a pressure on her and generally a bad idea. Some neediness would've been inevitably shown if I had gone down that road. Furthermore, traits of what I do not want to be but almost became would be present. I still take it as a fall to actually having thought about it, I understood my mistake. Don't know what came onto me to throw me into such useless deep thoughts, probably my ego that would take the hit and not being able to train, eat and rest properly for a few days which could've affected my psychological state a bit, aswell.
Chatted a bit today, keeping it light, some dirty stuff here and there. I have the upper hand on sex because she really likes it, so I'm using that. The most important - regained control over what we're doing, she tried to make me chase her and have the control. Tried to state she'd do whatever she wants in means of not behaving appropriately and not listening to me, I punished that and turned it around so now she's still chasing me. With me always being the one that leaves the conversation first, I finished off confusing her with the silver medal routine thing. She asked why isn't he getting a gold one for putting on her erotic underwear and coming in bed with me. I always get stuck when they ask that question, I usually ignore it. How would you react to the question? -Not that it matters that much but it won't hurt to know what you would come up with.

Say, sorry sweetie, you gotta work harder if you want that gold. Then change the subject.