Why do guys treat girls as if we were so disposable?

It seems that every guy I have in my life (whether its friends, or date, or whatever) always treat me like I am so disposable. I am there for them, even when they feel really sad of anything, ill be the best damn friend they can have, but when it comes to it, after a couple of weeks or whatever, they let me down, they won't call for a couple of weeks, when at the beginning I was like the flavor of the week, they'd be all exited to see me every two days

! I know some will say maybe they had something for you, but no we were talking about other girls! So what do I do wrong? Am I being too nice and being used for the time they feel down or whatever?
Why do guys treat girls as if we were so disposable?
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