have a serious crush on that girl, no more appetite, always feeling down and thinking of her, what should i do?

well have self control not normal self control of hands and feet but self control of feeling and mind the feeling you have right now is just imagination wanting her (more likely a lust) this may get a little complicated but you need to be a little cold hearted toward these feeling do you really wanna destroy relationship with your gf these feeling you talked about may cause you to desire her greater than your gf so be careful about those feeling if you dont take control of them soon they will bother you even more being a little cold hearted might help or just being simple minded like saying to your self she dont love me... might help too

First of all, EAT. Force feed yourself at least small meals. Just tell her straight up. It cant hurt you in anyway really. You wont get a yes without asking. Even if she doesnt like you back, the worst she can say is NO.