Hi buttons, I do know exactly how you feel.
However, I also think that the very way in which you've actually asked this means that you are self-aware, and not a rubbish friend at all! You must care about those close to you to reflect in this way.
I think good friends can always start up where they left off, and understand that just because you haven't spoken for a while, it doesn't mean the friendship is less valuable.
Just be honest with your friends: try and see them, either as a group if you're all mates, or individually, and explain why you've been a bit absent, and apologise. Tell them that in the coming future you'll try and be around more, and if you need their help or support, ASK them: it's what friends are for!
x