Do I expect too much from my friends?

I feel somewhat invisible to my friends. I am there for them, I listen to them when they’re down, when they’re happy/excited, etc.
My friends seem to enjoy spending time with me…when I’m happy, laid-back, etc.
However, if I hit a low point, they scarper. I honestly feel so lonely and rather disillusioned.
This isn’t true for all of my friends, but I wonder if I should just move on from the ones that cannot offer any support when I need it most?
I feel a small bit bitter about the fact that I willingly and lovingly give them my time, attention and energy, yet I don’t receive anything close in return.
Some input would be greatly appreciated