i only talking about the alst question now...
if nothing matters, what responsibility do we have?
because that is, by far, one of the most important questions in life...

there are people out there, who talk about niveau, webeing better than animals, some people are being smarter and thus better than other, and if you for example kill a murderer, youre nothing better than him...
but who cares anyway?

for all the wrong reasons, people, for centuries, belived that they are better than the rest of all those lives on this planet.
some think we deserve more rights than animals. some think we are better because we know how to use guns....

what responsibility do we have of nothing exists, if there is no god?
there is no real answer to that question. only my personal opinion. and thats, basically, the answer.
you are your responsibility, to you and yourself only.
can you live with the things you do, the consequences for your actions? or cant you.
nobody stops you from killing anyone. how could one. we dont know what you think, and this is good. although i hardly disagree with saying we have a free will, because for all we know, we dont, but i agree with saying we can do what we want.

so, lets get back to the question here.
first, lets define responsibility. anotehr one of those terms humans created for whatever reason.
it depends on what you want to be. ike good or evil, its always what we think we are.
a terrorist thinks he is good, same does the pope, or the little boy who gave a poor fella his sandwich. they all think they are the good guys.
so whats good and whats evil?

nietzsche once said, that the slave people speak in terms of good and evil, while the master people speak in terms of good and bad... he was right with that.

the question is, do you want to be good or bad? not good or evil. bad in a sense of bad for whatever you belive it might be.

for example, me. i want to be good for this generation. i want to show the people that they can live without killing each other. no silly liebral left winged multi culturism utopia that wont work. no. but just leaving others alone with whatever they are, and there is peace...

its simple. if all terrorists stop what they are doing and instead take care of themselves. if all warlords stop caring about who the damn has said anything to them. if all those naysayers and world-better-makers shut the hell up and instead take care of their own lives...
what would happen, if everybody just watches himself/herself and shuts the hell up?

i dont belive in god. or afterlife. or whatever. i belive that its my responsibility to live my live as happyly as i can without annoying anyone. i dont want to hurt anyone i dont want to save anyone. i just ant to be left alone.
and if everyone would do this, there wouldbe no need for saving. if someone needshelp, i help. but i dont run around telling people how to lvie their lives. i dotn try to save a few pooor souls froom themselves. its their problem. and my problems are mine. not yours. not anyones... mine...

so to answer your question about responsibility:
your own. you are your responsibility. you alone. nothing else. and whatever you do with that, is still your responsibility...