Recently (about two months ago), I started talking to this girl (I am a guy). We had more than a few nice conversations, and everything was going smoothly. She has a boyfriend, which I have no issue with. He’s a nice enough person, and I don’t dislike him at all.
I have developed some feelings for her, but I understand that nothing is going to happen (she’s already in a relationship). As such, I am totally okay with just being her friend.
However, she has blatantly ignored me for the past week, despite multiple attempts by me to reach out to her. I haven’t told her (or anyone else) about my feelings, but what I believe to be happening is that she inferred that I had feelings for her and wants to block me out.
Is there really anything I can do about this?
LemonVibe 
No.
When people we care about ignore us it can be miserable- recent research shows that when we sense rejection it the same parts of our brain are activated as when we are physically hurt. That said I can imagine this whole experience is quite unpleasant for you and there may be emotions that are impacting how you are looking at the situation.
Sometimes doing nothing is doing something, and this may be one of those times. Let things run their course- you may see her warm up later on.
Original poster back with an update:
I decided to try the “do nothing” method, and it turned out rather poorly. This girl now thinks even less of me, and we only speak occasionally. My feelings for her have died down, but only a little bit, and quite honestly I feel guilty talking to her, considering how often she mentions her boyfriend. It seems that there really wasn’t a great way to resolve the issue. Guess I’ll just have to live with it.
Do you have any idea why she would think less of you for “doing nothing”? I mean, it’s hard for me to imagine how doing nothing could cause her to shun you even more. Are you sure it wasn’t something that you just weren’t aware of?