Do I pursue him? he isnt being flirty?

[JDHoney]

I'm going to put in as much detail as possible, sorry if its boring. Im used to men mutually talking with me and us flirting, however, the guy i like at the moment doesnt, lets call him Ben. i realise this may be an indicator that he does not like me but ill just give some background.

he's in the same large group of friends as me, like over 100, as its a university society and I've met him a few times, every time I've met him I've said hi briefly and so has he, but ultimately he ends up talking to people he knows better and we don't speak that much. Recently we were at a similar gig and we got to talk a little there with a small group of friends and i saw this as an excuse to message him on facebook the next day.

this guy takes forever to reply, now he isn't on facebook a lot but he will reply every day or every other day. It seems bleak but i don't know whether to give up or not. Usually in given some kind of sign but I'm holding out hope that he's just not flirty at all. They aren't one word answers but i find myself asking questions just to keep the conversation going.

does anyone have any advice for me? Either on whether to give up or on how to get some alone time with him?

i always see him in a very large social setting so its not a one to one thing.