I have some sauce for you.To tell you about myself, I'm a former pickup artist guy and Navy veteran with a lot of experience in girling. What I did when I was in your shoes was I texted the girl I liked and I said, hey "Sarah, (random name)", I have some news you might not want to here. I'm just getting to know you in ways I hadn't thought I would and I want to be more than just your friend. I don't think hanging out in the future would be ideal as just friends and since you have a boyfriend I likely won't be around anymore. I'm so sorry to do this but I'm trying to take charge and live the kind of life I want to.

If she says anything other than "I like you too romantically", you could hit her with a follow-up statement about how friends shouldn't ever put each other in boxes and that relationship dynamics are in your opinion a bit of an antiquated system.

There is a book called "The Game", by Neil Strauss and it gives a pretty in-depth explanation of how one leaves the friend zone. Just don't stick around like a jaded cop because if she doesn't respect your ability to leave she won't see you as having higher value at all.

I completely understand what you're feeling brother, been there. In my opinion, you have two options. Tell her how you feel (after you have written it down, so that you can articulate it fully!) or take a step back and if that means telling her that you need some space (because you run in the same social circles/work together). Any other advice you get is going to be complex and non beneficial, because every situation is unique. there are commonalities, but its highly nuanced. This is the best advice to take because there is a potential to be with her without confusing and hurting your shared friendship. Be assertive or leave. 

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