Overly attached to my friend?

I have a friend who I think I’m overly attached to. We’re in our final year of sixth form, have been friends since year 7, and are quite close. I treat her really well. I always try to cheer her up, help her whenever possible, tell her she looks lovely, and sometimes even buy her things. And I feel like 70% of the time, my efforts are not reciprocated. There are periods of time where she’ll reciprocate and we’ll feel like the best friends on the entire planet. But a lot of the time, like today, she acts kind of off with me. I know one of the first comments is gonna be “stop doing those things for her if she doesn’t reciprocate.” But that’s my problem. I think I’m so attached to her that I literally can’t stop. I get really upset when she talks to me and doesn’t seem enthusiastic. I also take it personally when she’s in a bad mood and responds to me bluntly. I feel that it’s because I’m not trying hard enough as a friend. Which encourages me to try harder. Does anyone have any advice? I want to stop feeling like this. I want to be able to stand up for myself and stop being so attached to someone who clearly isn’t as attached to me. I just want us to be NORMAL friends.