It's hard when you put yourself out there and it doesn't work out. Even worse when it happens a few times in quick succession. This is something I have struggled with also, and because it has been painful, has stopped me initiating new friendships. Now I wait for others to give me a clear sign that they are interested, then I'm happy to act.
I too have friends that I have supported that haven't been able to do the same, and I have learned to accept that and keep the friendship at a more surface level. I do have a friend or two that never turn their backs on me, and thinking about them when I am hurt, even if for whatever reason I can't see them (live far away) helps me deal with other setbacks.
I'm sorry, I don't really have any advice for you, just wanted to let you know I understand.
I write to let my feelings out. Is there anything you can do to not let the pain build inside you?