Blame Me. I Don't Care

I don't think I can do this anymore. I want to let go and forget I even tried to make this work. I'm sure if I gave it a lot of time and energy, it would be worth it - but I just simply don't want to. I feel like I'm not making any progress by trying to make her be with me because in reality, we all know that can't happen. You can't make someone be with you nor force them to change how you feel. She has a boyfriend, and yet she has feelings for me to. Call me the bad guy if you want, but I'm not the one to fully blame for this. I'm not saying it's her fault, but I definitely don't want to put the blame on myself anymore. In the past few weeks, I've gone out of my way to flatter her, do things for her, and do everything I could to make her laugh and have a good time. I'm trying to show her that I care. She tells me I'm sweet and thoughtful and that I would be such a good boyfriend to her, yet does absolutely nothing to fix the situation.