Look man, i know how you feel, ive been in your position (not the creepy wallpaper shit, just liking a girl that doenst like me back). I know that prob nothing that i can say will help you, but ill try anyways.
1. FORGET ABOUT HER
Start by deleting this cringy wallpaper shit. Dont follow het on social media, just ignore her shit.
2. DO THINGS THAT MAKE YOU FEEL HAPPY
you can play games, play sports watch movies, anyway, ocupy your time with things that makes it easier to not think about this girl
3. IMPROVE YOURSELF
Hit the fucking gym, learn a new language, join a new class, get a tattoo idk
4. GO OUT AND FUCK SOME RANDOM BITCHES
Go to a bar w your friends, get wasted, if you dont find any sexy girl then just fuck any fat or ugly ones (pls not fat AND ugly).
Your life will be better if you quit this "feeling sorry for yourself cuz youre not ""man enough"" for this bitch" shit.